Arthur J. Gallagher & Co. (AJG) 10-K8 Feb 212020 FY Annual reportFinancial data

Company Profile

Cover Page

Cover Page - USD ($)	12 Months Ended
Cover Page - USD ($)	Dec. 31, 2020	Jan. 31, 2021	Jun. 30, 2020
Cover [Abstract]
Amendment Flag	false
Document Type	10-K
Document Fiscal Year Focus	2020
Entity Interactive Data Current	Yes
Document Fiscal Period Focus	FY
Document Annual Report	true
Entity Central Index Key	0000354190
Document Transition Report	false
Current Fiscal Year End Date	--12-31
Document Period End Date	Dec. 31, 2020
Entity Registrant Name	ARTHUR J. GALLAGHER & CO.
Entity File Number	1-09761
Entity Tax Identification Number	36-2151613
Entity Incorporation, State or Country Code	DE
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Address, Address Line One	2850 Golf Road
Entity Address, City or Town	Rolling Meadows
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60008-4050
City Area Code	630
Local Phone Number	773-3800
Trading Symbol	AJG
Security Exchange Name	NYSE
Title of 12(b) Security	Common Stock, par value $1.00 per share
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
ICFR Auditor Attestation Flag	true
Entity Public Float			$ 16,249,616,000
Entity Common Stock, Shares Outstanding		193,740,000
Documents Incorporated by Reference	Documents incorporated by reference: Portions of Arthur J. Gallagher & Co.’s definitive 2021 Proxy Statement are incorporated by reference into this Form 10‑K in response to Part III to the extent described herein.

Consolidated Statement of Earni

Consolidated Statement of Earnings - USD ($) $ in Millions	12 Months Ended
Consolidated Statement of Earnings - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues before reimbursements	$ 6,851.9	$ 7,056.4	$ 6,792.4
Reimbursements	151.7	138.6	141.6
Total revenues	7,003.6	7,195	6,934
Compensation	3,466.5	3,339.5	3,026.3
Operating	906.5	1,068.5	903.7
Reimbursements	151.7	138.6	141.6
Cost of revenues from clean coal activities	882.1	1,352.8	1,816
Interest	196.4	179.8	138.4
Depreciation	145.1	140.4	127.8
Amortization	417.3	334	291.2
Change in estimated acquisition earnout payables	(32.9)	15.3	9.6
Total expenses	6,132.7	6,568.9	6,454.6
Earnings before income taxes	870.9	626.1	479.4
Provision (benefit) for income taxes	12.8	(89.7)	(196.5)
Net earnings	858.1	715.8	675.9
Net earnings attributable to noncontrolling interests	39.3	47	42.4
Net earnings attributable to controlling interests	$ 818.8	$ 668.8	$ 633.5
Basic net earnings per share	$ 4.29	$ 3.60	$ 3.47
Diluted net earnings per share	4.20	3.52	3.40
Dividends declared per common share	$ 1.80	$ 1.72	$ 1.64
Commissions [Member]
Revenues before reimbursements	$ 3,591.9	$ 3,320.6	$ 2,920.7
Broker Fees [Member]
Revenues before reimbursements	1,957.9	1,911.1	1,756.3
Supplemental Revenue [Member]
Revenues before reimbursements	221.9	210.5	189.9
Contingent Revenue [Member]
Revenues before reimbursements	147	135.6	98
Investment income [Member]
Revenues before reimbursements	75.9	86.9	70.1
Net (Losses) Gains on Divestitures [Member]
Revenues before reimbursements	(5.8)	75.3	10.2
Clean Coal Activities [Member]
Revenues before reimbursements	863.5	1,319.3	1,746.3
Other net (losses) revenue [Member]
Revenues before reimbursements	$ (0.4)	$ (2.9)	$ 0.9

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Earnings - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net earnings	$ 858.1	$ 715.8	$ 675.9
Change in pension liability, net of taxes	0.4	4.7	(10.3)
Foreign currency translation, net of taxes in 2020 and 2019	183.7	44	(197.7)
Change in fair value of derivative instruments, net of taxes	(68.1)	(22.7)	(15.6)
Comprehensive earnings	974.1	741.8	452.3
Comprehensive earnings attributable to noncontrolling interests	39.7	47.3	40.4
Comprehensive earnings attributable to controlling interests	$ 934.4	$ 694.5	$ 411.9

Consolidated Balance Sheet

Consolidated Balance Sheet - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Cash and cash equivalents	$ 664.6	$ 604.8
Restricted cash	2,909.7	2,019.1
Premiums and fees receivable	6,436	5,419.2
Other current assets	1,113.9	1,074.4
Total current assets	11,124.2	9,117.5
Fixed assets - net	450.7	467.4
Deferred income taxes	1,085.8	945.6
Other noncurrent assets	769.9	773.6
Right-of-use assets	373.9	393.5
Goodwill - net	6,127	5,618.5
Amortizable intangible assets - net	2,399.9	2,318.7
Total assets	22,331.4	19,634.8
Premiums payable to underwriting enterprises	7,784.6	6,348.5
Accrued compensation and other accrued liabilities	1,596.2	1,347.8
Deferred revenue - current	475.6	434.1
Premium financing borrowings	203.6	170.6
Corporate related borrowings - current	75	620
Total current liabilities	10,135	8,921
Corporate related borrowings - noncurrent	4,266	3,816.1
Deferred revenue - noncurrent	65.7	69.7
Lease liabilities - noncurrent	320.9	340.9
Other noncurrent liabilities	1,311.1	1,271.6
Total liabilities	16,098.7	14,419.3
Stockholders' equity:
Common stock - authorized 400.0 shares; issued and outstanding 193.7 shares in 2020 and 188.1 shares in 2019	193.7	188.1
Capital in excess of par value	4,264.4	3,825.7
Retained earnings	2,371.7	1,901.3
Accumulated other comprehensive loss	(643.6)	(759.6)
Stockholders' equity attributable to controlling interests	6,186.2	5,155.5
Stockholders' equity attributable to noncontrolling interests	46.5	60
Total stockholders' equity	6,232.7	5,215.5
Total liabilities and stockholders' equity	$ 22,331.4	$ 19,634.8

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - shares	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Common stock - authorized shares	400,000,000	400,000,000
Common stock - issued shares	193,700,000	188,100,000
Common stock - outstanding shares	193,700,000	188,100,000

Consolidated Statement of Cash

Consolidated Statement of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net earnings	$ 858.1	$ 715.8	$ 675.9
Adjustments to reconcile net earnings to net cash provided by operating activities:
Net loss (gain) on investments and other	6.3	(72)	(8.4)
Depreciation and amortization	562.4	474.4	419
Change in estimated acquisition earnout payables	(32.9)	15.3	9.6
Amortization of deferred compensation and restricted stock	60.9	47.2	41.6
Stock-based and other noncash compensation expense	13.6	14	13.7
Payments on acquisition earnouts in excess of original estimates	(14.5)	(16.6)	(64.6)
Effect of changes in foreign exchange rate	2.9	6.7	(2.9)
Net change in premium and fees receivable	(796.5)	(434.7)	(783.1)
Net change in deferred revenue	18.5	12.8	18.4
Net change in premiums payable to underwriting enterprises	1,154.2	461.6	819.7
Net change in other current assets	(77.1)	(60.5)	(134.7)
Net change in accrued compensation and other accrued liabilities	91.8	77	44.9
Net change in income taxes payable	51.8	35.5	(46)
Net change in deferred income taxes	(175.6)	(150.7)	(216)
Net change in other noncurrent assets and liabilities	28.6	(6.6)	(22)
Net cash provided by operating activities	1,752.5	1,119.2	765.1
Cash flows from investing activities:
Capital expenditures	(99.3)	(138.8)	(124.4)
Cash paid for acquisitions, net of cash and restricted cash acquired	(324.3)	(1,266.8)	(784.8)
Net proceeds from sales of operations/books of business	8.2	81	14.5
Net funding of investment transactions	(1.4)	(52)	(15.6)
Net cash used by investing activities	(416.8)	(1,376.6)	(910.3)
Cash flows from financing activities:
Payments on acquisition earnouts	(38.8)	(46.3)	(62.1)
Proceeds from issuance of common stock	111.9	101.2	81.9
Repurchases of common stock			(11.3)
Payments to noncontrolling interests	(84.4)	(75.4)	(54.2)
Dividends paid	(347.4)	(321.1)	(301.8)
Net borrowings on premium financing debt facility	16	19.2	32.9
Borrowings on line of credit facility	2,630	4,315	3,075
Repayments on line of credit facility	(3,150)	(4,060)	(3,000)
Net borrowings of corporate related long-term debt	424.9	725	400
Debt acquisition costs	(1.3)	(3.9)	(1.3)
Settlements on terminated interest rate swaps	(66)	(15.3)	2.9
Net cash (used) provided by financing activities	(505.1)	638.4	162
Effect of changes in foreign exchange rates on cash, cash equivalents and restricted cash	119.8	6.1	(85)
Net increase (decrease) in cash, cash equivalents and restricted cash	950.4	387.1	(68.2)
Cash, cash equivalents and restricted cash at beginning of year	2,623.9	2,236.8	2,305
Cash, cash equivalents and restricted cash at end of year	$ 3,574.3	$ 2,623.9	$ 2,236.8

Consolidated Statement of Stock

Consolidated Statement of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Cumulative Effect Period Of Adoption Adjustment [Member]	Common Stock [Member]	Capital in Excess of Par Value [Member]	Retained Earnings [Member]	Retained Earnings [Member]Cumulative Effect Period Of Adoption Adjustment [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Other Comprehensive Loss [Member]Cumulative Effect Period Of Adoption Adjustment [Member]	Noncontrolling Interests [Member]
Beginning balance at Dec. 31, 2017	$ 4,299.7		$ 181	$ 3,388.2	$ 1,221.8		$ (555.4)		$ 64.1
Beginning balance (in shares) at Dec. 31, 2017			181
Reclassification of the income tax effects with in accumulated other comprehensive loss related to the TCJA					6.6		(6.6)
Net earnings	675.9				633.5				42.4
Net purchase of subsidiary shares from noncontrolling interests	(0.7)			(5)					4.3
Dividends paid to noncontrolling interests	(38)								(38)
Net change in pension asset/liability, net of taxes	(10.3)						(10.3)
Foreign currency translation	(199.7)						(197.7)		(2)
Change in fair value of derivative instruments, net of taxes	(15.6)						(15.6)
Compensation expense related to stock option plan grants	13.7			13.7
Common stock issued in: purchase transactions	61.6		$ 0.8	60.8
Common stock issued in: purchase transactions (in shares)			0.8
Stock option plans	58.6		$ 1.6	57
Stock option plans (in shares)			1.6
Employee stock purchase plan	23.3		$ 0.4	22.9
Employee stock purchase plan (in shares)			0.4
Deferred compensation and restricted stock	15.8		$ 0.3	15.5
Deferred compensation and restricted (in shares)			0.3
Common stock repurchases	(11.3)		$ (0.1)	(11.2)
Common stock repurchases (in shares)			(0.1)
Cash dividends declared on common stock	(303.3)				(303.3)
Ending balance at Dec. 31, 2018	4,569.7	$ (2.4)	$ 184	3,541.9	1,558.6	$ (2.2)	(785.6)	$ (0.2)	70.8
Ending balance (in shares) at Dec. 31, 2018			184
Net earnings	715.8				668.8				47
Net purchase of subsidiary shares from noncontrolling interests	(15.1)								(15.1)
Dividends paid to noncontrolling interests	(43)								(43)
Net change in pension asset/liability, net of taxes	4.7						4.7
Foreign currency translation	44.5						44.2		0.3
Change in fair value of derivative instruments, net of taxes	(22.7)						(22.7)
Compensation expense related to stock option plan grants	14			14
Common stock issued in: purchase transactions	168		$ 1.9	166.1
Common stock issued in: purchase transactions (in shares)			1.9
Stock option plans	$ 73.7		$ 1.8	71.9
Stock option plans (in shares)	1.9		1.8
Employee stock purchase plan	$ 27.5		$ 0.3	27.2
Employee stock purchase plan (in shares)			0.3
Deferred compensation and restricted stock	4.7		$ 0.1	4.6
Deferred compensation and restricted (in shares)			0.1
Cash dividends declared on common stock	(323.9)				(323.9)
Ending balance at Dec. 31, 2019	$ 5,215.5		$ 188.1	3,825.7	1,901.3		(759.6)		60
Ending balance (in shares) at Dec. 31, 2019	188.1		188.1
Net earnings	$ 858.1				818.8				39.3
Net purchase of subsidiary shares from noncontrolling interests	(6.4)								(6.4)
Dividends paid to noncontrolling interests	(46.8)								(46.8)
Net change in pension asset/liability, net of taxes	0.4						0.4
Foreign currency translation	184.1						183.7		0.4
Change in fair value of derivative instruments, net of taxes	(68.1)						(68.1)
Compensation expense related to stock option plan grants	13.6			13.6
Common stock issued in: purchase transactions	309.1		$ 3	306.1
Common stock issued in: purchase transactions (in shares)			3
Stock option plans	$ 77.7		$ 1.8	75.9
Stock option plans (in shares)	1.8		1.8
Employee stock purchase plan	$ 34.2		$ 0.5	33.7
Employee stock purchase plan (in shares)			0.5
Deferred compensation and restricted stock	9.7		$ 0.3	9.4
Deferred compensation and restricted (in shares)			0.3
Cash dividends declared on common stock	(348.4)				(348.4)
Ending balance at Dec. 31, 2020	$ 6,232.7		$ 193.7	$ 4,264.4	$ 2,371.7		$ (643.6)		$ 46.5
Ending balance (in shares) at Dec. 31, 2020	193.7		193.7

Consolidated Statement of Sto_2

Consolidated Statement of Stockholders' Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Stockholders Equity [Abstract]
Tax effect on net change in pension asset/liability	$ 0.1	$ 1.1	$ 6.2
Net change in fair value of derivative instruments, tax	$ (22.4)	$ (8.9)	$ (5.6)

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	1. Summary of Significant Accounting Policies Terms Used in Notes to Consolidated Financial Statements ASC - Accounting Standards Codification. ASU - Accounting Standards Update. FASB - The Financial Accounting Standards Board. GAAP - U.S. generally accepted accounting principles. IRC - Internal Revenue Code. IRS - Internal Revenue Service. Topic 606 - ASU No. 2014-09, Revenue from Contracts with Customers. Underwriting enterprises - Insurance companies, reinsurance companies and various other forms of risk-taking entities, including intermediaries of underwriting enterprises. VIE - Variable interest entity. Nature of Operations Arthur J. Gallagher & Co. and its subsidiaries, collectively referred to herein as we, our, us or the company, provide insurance brokerage, consulting and third party claims settlement and administration services to both domestic and international entities. We have three reportable segments: brokerage, risk management and corporate. Our brokers, agents and administrators act as intermediaries between and our clients. Our brokerage segment operations provide brokerage and consulting services to companies and entities of all types, including commercial, not-for-profit, public entities, and, to a lesser extent, individuals, in the areas of insurance placement, risk of loss management, and management of employer sponsored benefit programs. Our risk management segment operations provide contract claim settlement, claim administration, loss control services and risk management consulting for commercial, not‑for‑profit, captive and public entities, and various other organizations that choose to self-insure property/casualty coverages or choose to use a third-party claims management organization rather than the claim services provided by underwriting enterprises. The corporate segment reports the financial information related to our debt and other corporate costs, clean energy investments, external acquisition-related expenses and the impact of foreign currency translation. Clean energy investments consist of our investments in limited liability companies that own 35 commercial clean coal production facilities producing refined coal using Chem-Mod LLC’s proprietary technologies. We believe these operations produce refined coal that qualifies for tax credits under IRC Section 45. We do not assume underwriting risk on a net basis, other than with respect to de minimis amounts necessary to provide minimum or regulatory capital to organize captives, pools, specialized underwriters or risk-retention groups. Rather, capital necessary for covering losses is provided by underwriting enterprises. Investment income and other revenues are primarily generated from our premium financing operations, our invested cash and restricted cash we hold on behalf of our clients, as well as clean energy investments. In addition, our share of the net earnings related to partially owned entities that are accounted for using the equity method is included in investment income. We are headquartered in Rolling Meadows, Illinois, have operations in 49 countries and offer client-service capabilities in more than 150 countries globally through a network of correspondent insurance brokers and consultants. Basis of Presentation The accompanying consolidated financial statements include our accounts and all of our majority-owned subsidiaries (50% or greater ownership). Substantially all of our investments in partially owned entities in which our ownership is less than 50% are accounted for using the equity method based on the legal form of our ownership interest and the applicable ownership percentage of the entity. However, in situations where a less than 50%-owned investment has been determined to be a VIE and we are deemed to be the primary beneficiary in accordance with the variable interest model of consolidation, we will consolidate the investment into our consolidated financial statements. For partially owned entities accounted for using the equity method, our share of the net earnings of these entities is included in consolidated net earnings. All material intercompany accounts and transactions have been eliminated in consolidation. In the preparation of our consolidated financial statements as of December 31, 2020, management evaluated all material subsequent events or transactions that occurred after the balance sheet date through the date on which the financial statements were issued for potential recognition and/or disclosure in the notes therein. Use of Estimates The preparation of our consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. These accounting principles require us to make estimates and assumptions that affect the reported amounts of assets and liabilities and revenues and expenses, and the disclosure of contingent assets and liabilities at the date of our consolidated financial statements. We periodically evaluate our estimates and assumptions, including those relating to the valuation of goodwill and other intangible assets, right-of-use assets, investments (including our IRC Section 45 investments), income taxes, revenue recognition, deferred costs, stock-based compensation, claims handling obligations, retirement plans, litigation and contingencies. We base our estimates on historical experience and various assumptions that we believe to be reasonable based on specific circumstances. Such estimates and assumptions could change in the future as more information becomes known, which could impact the amounts reported and disclosed herein. Revenue Recognition Our revenues are derived from commissions and fees as primarily specified in a written contract, or unwritten business understanding, with our clients or underwriting enterprises. We also recognize investment income over time from our invested assets and invested assets we hold on behalf of our clients or underwriting enterprises. BROKERAGE SEGMENT Our brokerage segment generates revenues by: (i) Identifying, negotiating and placing all forms of insurance or reinsurance coverage, as well as providing risk-shifting, risk-sharing and risk-mitigation consulting services, principally related to property/casualty, life, health, welfare and disability insurance. We also provide these services through, or in conjunction with, other unrelated agents and brokers, consultants and management advisors. (ii) Acting as an agent or broker for multiple underwriting enterprises by providing services such as sales, marketing, selecting, negotiating, underwriting, servicing and placing insurance coverage on their behalf. (iii) Providing consulting services related to health and welfare benefits, voluntary benefits, executive benefits, compensation, retirement planning, institutional investment and fiduciary, actuarial, compliance, private insurance exchange, human resource technology, communications and benefits administration. (iv) Providing management and administrative services to captives, pools, risk-retention groups, healthcare exchanges, small underwriting enterprises, such as accounting, claims and loss processing assistance, feasibility studies, actuarial studies, data analytics and other administrative services. The vast majority of our brokerage contracts and service understandings are for a period of one year or less. Commissions and fees The primary source of revenues for our brokerage services is commissions from underwriting enterprises, based on a percentage of premiums paid by our clients, or fees received from clients based on an agreed level of service usually in lieu of commissions. These commissions and fees revenues are substantially recognized at a point in time on the effective date of the associated policies when control of the policy transfers to the client, as well as deferring certain revenues to reflect delivery of services over the contract period. Commissions are fixed at the contract effective date and generally are based on a percentage of premiums for insurance coverage or employee headcount for employer sponsored benefit plans. Commissions depend upon a large number of factors, including the type of risk being placed, the particular underwriting enterprise’s demand, the expected loss experience of the particular risk of coverage, and historical benchmarks surrounding the level of effort necessary for us to place and service the insurance contract. Rather than being tied to the amount of premiums, fees are most often based on an expected level of effort to provide our services. Whether we are paid a commission or a fee, the vast majority of our services are associated with the placement of an insurance (or insurance-like) contract. Accordingly, we recognize approximately 80% of our commission and fee revenues on the effective date of the underlying insurance contract. The amount of revenue we recognize is based on our costs to provide our services up and through that effective date, including an appropriate estimate of our profit margin on a portfolio basis (a practical expedient as defined in Topic 606). Based on the proportion of additional services we provide in each period after the effective date of the insurance contract, including an appropriate estimate of our profit margin, we recognize approximately 15% of our commission and fee revenues in the first three months, and the remaining 5% thereafter. These periods may be different than the underlying premium payment patterns of the insurance contracts, but the vast majority of our services are fully provided within one year of the insurance contract effective date. For consulting and advisory services, we recognize our revenue in the period in which we provide the service or advice. For management and administrative services, our revenue is recognized ratably over the contract period consistent with the performance of our obligations, mostly over an annual term. Supplemental revenues Certain underwriting enterprises may pay us additional revenues for the volume of premium placed with them and for insights into our sales pipeline, our sales capabilities or our risk selection knowledge. These amounts are in excess of the commission and fee revenues discussed above, and not all business we place with underwriting enterprises is eligible for supplemental revenues. Unlike contingent revenues, discussed below, these revenues are primarily a fixed amount or fixed percentage of premium of the underlying eligible insurance contracts. For supplemental revenue contracts based on a fixed percentage of premium, our obligation to the underwriting enterprise is substantially completed upon the effective date of the underlying insurance contract and revenue is fully earned at that time. For supplemental revenue contracts based on a fixed amount, revenue is recognized ratably over the contract period consistent with the performance of our obligations, almost always over an annual term. We receive these revenues on a quarterly or annual basis. Contingent revenues Certain underwriting enterprises may pay us additional revenues for our sales capabilities, our risk selection knowledge, or our administrative efficiencies. These amounts are in excess of the commission or fee revenues discussed above, and not all business we place with participating underwriting enterprises is eligible for contingent revenues. Unlike supplemental revenues, also discussed above, these revenues are variable, generally based on growth, the loss experience of the underlying insurance contracts, and/or our efficiency in processing the business. We generally operate under calendar year contracts, but we do not receive these revenues from the underwriting enterprises until the following calendar year, generally in the first and second quarters, after verification of the performance indicators outlined in the contracts. Accordingly, during each reporting period, we must make our best estimate of amounts we have earned using historical averages and other factors to project such revenues. We base our estimates each period on a contract-by-contract basis where available. In certain cases, it is impractical to assess a very large number of smaller contingent revenue contracts, so we use a historical portfolio estimate in aggregate (a practical expedient as defined in Topic 606). Because our expectation of the ultimate contingent revenue amounts to be earned can vary from period to period, especially in contracts sensitive to loss ratios, our estimates might change significantly from quarter to quarter. For example, in circumstances where our revenues are dependent on a full calendar year loss ratio, adverse loss experience in the fourth quarter could not only negate revenue earnings in the fourth quarter, but also trigger the need to reverse revenues previously recognized during the prior quarters. Variable consideration is recognized when we conclude, based on all the facts and information available at the reporting date, that it is probable that a significant revenue reversal will not occur in future periods. Sub-b rokerage costs Sub-brokerage costs are excluded from our gross revenues in our determination of total revenues. Sub-brokerage cost represents commissions paid to sub-brokers related to the placement of certain business by our brokerage segment operations. We recognize this contra revenue RISK MANAGEMENT SEGMENT Revenues for our risk management segment are comprised of fees generally negotiated (i) on a per-claim basis, (ii) on a cost‑plus basis, or (iii) as performance-based fees. We also provide risk management consulting services that are recognized as the services are delivered. Per-claim fees Where we operate under a contract with our fee established on a per-claim basis, our obligation is to process claims for a term specified within the contract. Because it is impractical to recognize our revenues on an individual claim-by-claim basis, we recognize revenue plus an appropriate estimate of our profit margin on a portfolio basis by grouping claims with similar characteristics (a practical expedient as defined in Topic 606). We apply actuarially-determined, historical-based patterns to determine our future service obligations, without applying a present value discount. Cost-plus fees Where we provide services and generate revenues on a cost-plus basis, we recognize revenue over the contract period consistent with the performance of our obligations. Performance-based fees Certain clients pay us additional fee revenues for our efficiency in managing claims or on the basis of claim outcome effectiveness. These amounts are in excess of the fee revenues discussed above. These revenues are variable, generally based on performance metrics set forth in the underlying contracts. We generally operate under multi-year contracts with fiscal year measurement periods. We do not receive these fees, if earned, until the following year after verification of the performance metrics outlined in the contracts. Each period we base our estimates on a contract-by-contract basis. We must make our best estimate of amounts we have earned using historical averages and other factors to project such revenues. Variable consideration is recognized when we conclude that is it probable that a significant revenue reversal will not occur in future periods. Reimbursements Reimbursements represent amounts received from clients reimbursing us for certain third-party costs associated with providing our claims management services. In certain service partner relationships, we are considered a principal because we direct the third party, control the specified service and combine the services provided into an integrated solution. Given this principal relationship, we are required to recognize revenue gross and service partner vendor fees in the operating expense in our consolidated statement of earnings. Deferred Costs We incur costs to provide brokerage and risk management services. Those costs are either (i) costs to obtain a contract or (ii) costs to fulfill such contract, or (iii) all other costs. (i) Costs to obtain - we incur costs to obtain a contract with a client. Those costs would not have been incurred if the contract had not been obtained. Almost all of our costs to obtain are incurred prior to, or on, the effective date of the contract and consist primarily of incentive compensation we pay to our production employees. Our costs to obtain are expensed as incurred as described in Note 4 to these consolidated financial statements. (ii) Costs to fulfill - we incur costs to fulfill a contract (or anticipated contract) with a client. Those costs are incurred prior to the effective date of the contract and relate to fulfilling our primary placement obligations to our clients. Our costs to fulfill prior to the effective date are capitalized and amortized on the effective date. These fulfillment activities include collecting underwriting information from our client, assessing their insurance needs and negotiating their placement with one or more underwriting enterprises. The majority of costs that we incur relate to compensation and benefits of our client service employees. Costs incurred during preplacement activities are expected to be recovered in the future. If the capitalized costs are no longer deemed to be recoverable, then they would be expensed. (iii) Other costs that are not costs to obtain or fulfill are expensed as incurred. Examples include other operating costs such as rent, utilities, management costs, overhead costs, legal and other professional fees, technology costs, insurance related costs, communication and advertising, and travel and entertainment. Depreciation, amortization and change in estimated acquisition earnout payable are expensed as incurred. Investment income Investment income primarily includes interest and dividend income (including interest income from our premium financing operations), which is accrued as it is earned. Net gains on divestitures represent one-time gains related to sales of brokerage related businesses, which are primarily recognized on a cash received basis. Revenues from clean coal activities include revenues from consolidated clean coal production plants, royalty income from clean coal licenses and income (loss) related to unconsolidated clean coal production plants, all of which are recognized as earned. Revenues from consolidated clean coal production plants represent sales of refined coal. Royalty income from clean coal licenses represents fee income related to the use of clean coal technologies. Income (loss) from unconsolidated clean coal production plants includes losses related to our equity portion of the pretax results of the clean coal production plants. Earnings per Share Basic net earnings per share is computed by dividing net earnings by the weighted average number of common shares outstanding during the reporting period. Diluted net earnings per share is computed by dividing net earnings by the weighted average number of common and common equivalent shares outstanding during the reporting period. Common equivalent shares include incremental shares from dilutive stock options, which are calculated from the date of grant under the treasury stock method using the average market price for the period. Cash and Cash Equivalents Short-term investments, consisting principally of cash and money market accounts that have average maturities of 90 days or less, are considered cash equivalents. Restricted Cash In our capacity as an insurance broker, we collect premiums from insureds and, after deducting our commissions and/or fees, remit these premiums to underwriting enterprises underwriting enterprises Related to our third party administration business and in certain of our brokerage operations, we are responsible for client claim funds that we hold in a fiduciary capacity. We do not earn any interest income on the funds held. These client funds have been included in restricted cash, along with a corresponding liability in premiums payable to underwriting enterprises Premiums and fees receivable Premiums and fees receivable in the accompanying consolidated balance sheet are net of allowances for estimated policy cancellations and doubtful accounts. The allowance for estimated policy cancellations was $9.9 million and $8.3 million at December 31, 2020 and 2019, respectively, which represents a reserve for future reversals in commission and fee revenues related to the potential cancellation of client insurance policies that were in force as of each year end. The allowance for doubtful accounts was $10.1 million and $8.7 million at December 31, 2020 and 2019, respectively. We establish the allowance for estimated policy cancellations through a charge to revenues and the allowance for doubtful accounts through a charge to operating expenses. Both of these allowances are based on estimates and assumptions using historical data to project future experience. Such estimates and assumptions could change in the future as more information becomes known which could impact the amounts reported and disclosed herein. We periodically review the adequacy of these allowances and make adjustments as necessary. Derivative Instruments We are exposed to market risks, including changes in foreign currency exchange rates and interest rates. To manage the risk related to these exposures, we enter into various derivative instruments that reduce these risks by creating offsetting exposures. In the normal course of business, we are exposed to the impact of foreign currency fluctuations that impact our results of operations and cash flows. We utilize a foreign currency risk management program involving foreign currency derivatives that consist of several monthly put/call options designed to hedge a portion of our future foreign currency disbursements through various future payment dates. To mitigate the counterparty credit risk we only enter into contracts with major financial institutions based upon their credit ratings and other factors. These derivative instrument contracts are cash flow hedges that qualify for hedge accounting and primarily hedge against fluctuations between changes in the GBP and Indian Rupee versus the U.S. dollar. Changes in fair value of the derivative instruments are reflected in other comprehensive earnings in the accompanying consolidated balance sheet. The impact of the hedge at maturity is recognized in the income statement as a component of investment income, compensation and operating expenses depending on the nature of the hedged item. We enter into various long-term debt agreements. We use interest rate derivatives, typically swaps, to reduce our exposure to the effects of interest rate fluctuations on the forecasted interest rates for up to three years into the future. These derivative instrument contracts are periodically monitored for hedge ineffectiveness, the amount of which has not been material to the accompanying consolidated financial statements. We do not use derivatives for trading or speculative purposes. Premium Financing Seven subsidiaries of the brokerage segment make short-term loans (generally with terms of twelve months or less) to our clients to finance premiums. These premium financing contracts are structured to minimize potential bad debt expense to us. Such receivables are generally considered delinquent after seven days of the payment due date. In normal course, insurance policies are cancelled within one month of the contractual payment due date if the payment remains delinquent. We recognize interest income as it is earned over the life of the contract using the “level-yield” method. Unearned interest related to contracts receivable is included in the receivable balance in the accompanying consolidated balance sheet. The outstanding loan receivable balance was $442.7 million and $388.1 million at December 31, 2020 and 2019, respectively. Fixed Assets We carry fixed assets at cost, less accumulated depreciation, in the accompanying consolidated balance sheet. We periodically review long-lived assets for impairment whenever events or changes in business circumstances indicate that the carrying value of the assets may not be recoverable. Under those circumstances, if the fair value were less than the carrying amount of the asset, we would recognize a loss for the difference. Depreciation for fixed assets is computed using the straight-line method over the following estimated useful lives: Useful Life Office equipment Three to ten years Furniture and fixtures Three to ten years Computer equipment Three to five years Building Fifteen to forty years Software Three to five years Refined fuel plants Ten years Leasehold improvements Shorter of the lease term or useful life of the asset Intangible Assets Intangible assets represent the excess of cost over the estimated fair value of net tangible assets of acquired businesses. Our primary intangible assets are classified as either goodwill, expiration lists, non-compete agreements or trade names. Expiration lists, non-compete agreements and trade names are amortized using the straight-line method over their estimated useful lives (two to fifteen years for expiration lists, two to six years for non-compete agreements and two to fifteen years for trade names), while goodwill is not subject to amortization. The establishment of goodwill, expiration lists, non-compete agreements and trade names and the determination of estimated useful lives are primarily based on valuations we receive from qualified independent appraisers. The calculations of these amounts are based on estimates and assumptions using historical and projected financial information and recognized valuation methods. Different estimates or assumptions could produce different results. We carry identifiable intangible assets at cost, less accumulated amortization, in the accompanying consolidated balance sheet. We review all of our intangible assets for impairment periodically (at least annually for goodwill) and whenever events or changes in business circumstances indicate that the carrying value of the assets may not be recoverable. We perform such impairment reviews at the division (i.e., reporting unit) level with respect to goodwill and at the business unit level for amortizable intangible assets. While goodwill is not amortizable, it is tested for impairment at least annually in the fourth quarter, and more frequently if there are indicators of impairment or whenever business circumstances suggest that the carrying value of goodwill may not be recoverable. We may initially perform a qualitative analysis to determine if it is more likely than not that the goodwill balance is impaired. If a qualitative assessment is not performed or if a The carrying value of amortizable intangible assets attributable to each business or asset group is periodically reviewed by management to determine if there are events or changes in circumstances that would indicate that its carrying amount may not be recoverable. Accordingly, if there are any such changes in circumstances during the year, we assess the carrying value of the amortizable intangible assets by considering the estimated future undiscounted cash flows generated by the corresponding business or asset group. Any impairment identified through this assessment may require that the carrying value of related amortizable intangible assets be adjusted and charged against current period earnings as a component of amortization expense. Based on the results of impairment reviews in 2020, 2019 and 2018, we wrote off $51.7 million, $0.1 million and $10.6 million, respectively, of amortizable intangible assets primarily related to prior year acquisitions of our brokerage and risk management segments, which is included in amortization expense in the accompanying consolidated statement of earnings. Income Taxes Our tax rate reflects the statutory tax rates applicable to our taxable earnings and tax planning in the various jurisdictions in which we operate. Significant judgment is required in determining the annual effective tax rate and in evaluating uncertain tax positions. We report a liability for unrecognized tax benefits resulting from uncertain tax positions taken or expected to be taken in our tax return. We evaluate our tax positions using a two-step process. The first step involves recognition. We determine whether it is more likely than not that a tax position will be sustained upon tax examination based solely on the technical merits of the position. The technical merits of a tax position are derived from both statutory and judicial authority (legislation and statutes, legislative intent, regulations, rulings and case law) and their applicability to the facts and circumstances of the position. If a tax position does not meet the “more likely than not” recognition threshold, we do not recognize the benefit of that position in the financial statements. The second step is measurement. A tax position that meets the “more likely than not” recognition threshold is measured to determine the amount of benefit to recognize in the financial statements. The tax position is measured as the largest amount of benefit that has a likelihood of greater than 50% of being realized upon ultimate resolution with a taxing authority. Uncertain tax positions are measured based upon the facts and circumstances that exist at each reporting period and involve significant management judgment. Subsequent changes in judgment based upon new information may lead to changes in recognition, derecognition and measurement. Adjustments may result, for example, upon resolution of an issue with the taxing authorities, or expiration of a statute of limitations barring an assessment for an issue. We recognize interest and penalties, if any, related to unrecognized tax benefits in our provision for income taxes. Tax law requires certain items to be included in our tax returns at different times than such items are reflected in the financial statements. As a result, the annual tax expense reflected in our consolidated statements of earnings is different than that reported in our tax returns. Some of these differences are permanent, such as expenses that are not deductible in our tax returns, and some differences are temporary and reverse over time, such as depreciation expense and amortization expense deductible for income tax purposes. Temporary differences create deferred tax assets and liabilities. Deferred tax liabilities generally represent tax expense recognized in the financial statements for which a tax payment has been deferred, or expense which has been deducted in the tax return but has not yet been recognized in the financial statements. Deferred tax assets generally represent items that can be used as a tax deduction or credit in tax returns in future years for which a benefit has already been recorded in the financial statements. We establish or adjust valuation allowances for deferred tax assets when we estimate that it is more likely than not that future taxable income will be insufficient to fully use a deduction or credit in a specific jurisdiction. In assessing the need for the recognition of a valuation allowance for deferred tax assets, we consider whether it is more likely than not that some portion, or all, of the deferred tax assets will not be realized and adjust the valuation allowance accordingly. We evaluate all significant available positive and negative evidence as part of our analysis. Negative evidence includes the existence of losses in recent years. Positive evidence includes the forecast of future taxable income by jurisdiction, tax-planning strategies that would result in the realization of deferred tax assets and the presence of taxable income in prior carryback years. The underlying assumptions we use in forecasting future taxable income require significant judgment and take into account our recent performance. Such estimates and assumptions could change in the future as more information becomes known which could impact the amounts reported and disclosed herein. The ultimate realization of deferred tax assets depends on the generation of future taxable income during the periods in which temporary differences are deductible or creditable. Fair Value of Financial Instruments Fair value accounting establishes a framework for measuring fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurem

Effect of New Accounting Pronou

Effect of New Accounting Pronouncements	12 Months Ended
Effect of New Accounting Pronouncements	Dec. 31, 2020
Accounting Changes And Error Corrections [Abstract]
Effect of New Accounting Pronouncements	2. Effect of New Accounting Pronouncements Leases In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). Under this new accounting guidance, an entity is required to recognize right-of-use assets and lease liabilities on its balance sheet and disclose key information about leasing ar We adopted ASC Topic 842 for all leases effective January 1, 2019, using the modified retrospective approach allowing us to initially apply the new lease standard at the adoption date and recognize a cumulative effect adjustment to the opening balance of retained earnings in the first quarter of 2019. Consequently, the reporting for the comparative prior year periods presented in 2019 will continue to be in accordance with the previous lease guidance under ASC Topic 840, including comparative disclosure requirements. We elected the package of practical expedients to carry forward historical identification and classification of leases that commenced before January 1, 2019 and to not re-assess initial direct costs for leases commencing before January 1, 2019. We also elected the lessee practical expedient, by class of underlying asset (e.g., office space), to not separate non-lease components such as lessor-provided maintenance and property management services from the associated lease component. The new lease accounting standard requires us to recognize lease right-of-use assets and lease liabilities on our balance sheet, which are established at the inception of a lease by computing a net present value of the future lease payments. Right-of-use assets are amortized to expense, and the discount amount related to lease liabilities is accreted to expense, over the lease term. The amortization of the right-of-use asset is calculated as the difference between the straight-line lease expense and the interest calculated on the lease liability. Rent payments are applied against the lease liabilities. Adoption of the new standard resulted in the recording of net right-of-use assets and lease liabilities of approximately $379.6 million and $420.3 million, respectively, and the reclassification of net rent related assets and liabilities of $38.3 million as of January 1, 2019. The difference between the additional lease assets and lease liabilities, net of the deferred tax impact, was recorded as a decrease to beginning retained earnings of $2.4 million. The adoption of the new standard had a de minimis impact on our consolidated statement of earnings and had no impact on our consolidated statement of cash flows. See Notes 15 and 17 Credit Impairment In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. Under the new guidance an entity is required to measure all credit losses on certain financial instruments, including trade receivables and various off-balance sheet credit exposures, using an expected credit loss model. This model incorporates past experience, current conditions and reasonable and supportable forecasts affecting collectability of these instruments. An entity will apply the new guidance through a cumulative-effect adjustment to retained earnings as of the beginning of the year of adoption. We adopted this new guidance effective January 1, 2020 and applied the guidance to measure credit losses on our financial instruments, which included premiums and fees receivable, premium finance advances and reinsurance recoverables. The adoption did not have a material impact on our consolidated financial statements. Disclosure Framework In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement. This new guidance modifies various disclosure requirements for fair value measurements, including in certain part those related to Level 3 fair value measurements. The new guidance was effective January 1, 2020. Certain portions of the guidance needed to be adopted prospectively while other portions were required to be adopted retrospectively for all periods presented. In August 2018, the FASB also issued ASU No. 2018-14, Compensation-Retirement Benefits-Defined Benefit Plans-General (Topic 715-20): Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans. This new guidance modifies various disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans. The new guidance was effective January 1, 2020, with early adoption permitted. Retrospective adoption is required. We adopted both of the standards effective January 1, 2020. The adoption did not have any impact on our consolidated financial statements. Hedge Accounting In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. The new guidance amends the hedge accounting model in the current guidance to enable entities to better portray the economics of their risk management activities in the financial statements and enhance the transparency and understandability of hedge results. The new guidance requires revised tabular disclosures that focus on the effect of hedge accounting by income statement line and the disclosure of the cumulative basis adjustments to the hedged assets and liabilities in fair value hedges. Certain additional disclosures are also required for hedge relationships designated under the last-of-layer method. The current guidance that requires entities to disclose hedge ineffectiveness has been eliminated because this amount will no longer be separately measured. Under the new guidance, entities will apply the amendments to cash flow and net investment hedge relationships that exist on the date of adoption using a modified retrospective approach (i.e., with a cumulative effect adjustment recorded to the opening balance of retained earnings as of the initial application date). The new guidance also provides transition relief to make it easier for entities to apply certain amendments to existing hedges (including fair value hedges) where the hedge documentation needs to be modified. The presentation and disclosure requirements will be applied prospectively. We adopted ASU 2017-12 on January 1, 2019. In accordance with the transition provisions of ASU 2017-12, we modified the recognition model for the excluded component from a mark-to-market approach to an amortization approach for our cash flow hedges with forward points existing as of the adoption date. The cumulative-effect related to this change resulted in an adjustment of $0.2 million that reduced accumulated other comprehensive income with a corresponding adjustment that increased retained earnings. See Note 16 for disclosures relating to our derivative and hedging activities. Intangibles - Goodwill and Other In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. The new guidance eliminates Step 2 of the goodwill impairment test. Instead, the updated guidance requires an entity to perform its annual or interim goodwill impairment test by comparing the fair value of the reporting unit to its carrying value, and recognizing a non-cash impairment charge for the amount by which the carrying value exceeds the reporting unit’s fair value with the loss not exceeding the total amount of goodwill allocated to that reporting unit. We adopted this new guidance effective January 1, 2020. The adoption did not have any impact on our consolidated financial statements. Internal-use Software In August 2018, the FASB issued ASU No. 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. This new accounting guidance requires deferral of certain implementation costs associated with a cloud computing arrangement, or hosting arrangement, thereby aligning deferral of such costs with implementation costs associated with developing internal-use software. Accounting for the service component of a hosting arrangement remains unchanged. An entity will defer these implementation costs over the term of the hosting arrangement, including optional renewal periods that are reasonably certain of exercise. Amounts expensed would be presented through operating expense, rather than depreciation or amortization. The new guidance was effective January 1, 2020. An entity may adopt the guidance either prospectively for all cloud computing arrangement implementation costs incurred on or after the effective date or retrospectively, including comparative periods. We adopted this new guidance effective January 1, 2020 on a prospective basis. The adoption did not have a material impact on our consolidated financial statements.

Business Combinations

Business Combinations	12 Months Ended
Business Combinations	Dec. 31, 2020
Business Combinations [Abstract]
Business Combinations	3. Business Combinations During 2020, we acquired substantially all of the net assets of the following firms in exchange for our common stock and/or cash. These acquisitions have been accounted for using the acquisition method for recording business combinations (in millions, except share data): Name and Effective Date of Acquisition Common Shares Issued Common Share Value Cash Paid Accrued Liability Escrow Deposited Recorded Earnout Payable Total Recorded Purchase Price Maximum Potential Earnout Payable (000s) Capsicum Reinsurance Brokers LLP (CRB) January 1, 2020 584 $ 62.9 $ 64.5 $ - $ - $ 129.9 $ 257.3 $ 209.1 Hanover Excess & Surplus, Inc. and Hanover Premium Finance, Inc. (HES) January 1, 2020 - - 30.1 - 3.0 - 33.1 9.3 CRES Insurance Services, LLC (CRES) June 1, 2020 288 28.5 1.5 - 1.0 5.5 36.5 7.3 Optimum Talent Inc. (OTI) November 1, 2020 102 11.1 14.1 - 3.4 14.0 42.6 21.1 Cool Insuring Agency, Inc. (CIA) December 1, 2020 406 48.4 65.0 - 7.2 8.5 129.1 30.0 Harden & Associates, Inc. (HAI) December 1, 2020 49 - 95.6 - 6.2 10.0 111.8 22.5 Ashton Tiffany, LLC (AT) December 31, 2020 - - 48.3 48.2 - 9.0 105.5 20.0 Twenty other acquisitions completed in 2020 414 38.8 79.2 1.8 9.9 30.5 160.2 68.6 1,843 $ 189.7 $ 398.3 $ 50.0 $ 30.7 $ 207.4 $ 876.1 $ 387.9 On December 23, 2020, we signed a definitive agreement to acquire 100% of the equity of The Bollington Wilson Group (which we refer to as Bollington) headquartered in Sale, Greater Manchester, U.K., for approximately $330.0 million of cash consideration. Bollington is a specialist U.K. insurance broker that has more than 400 employees and operates from a network of seven offices in the U.K. The transaction is subject to regulatory approval, which was received on January 26, 2021, and is expected to close in February 2021. Common shares issued in connection with acquisitions are valued at closing market prices as of the effective date of the applicable acquisition or on the days when the shares are issued, if purchase consideration is deferred. We record escrow deposits that are returned to us as a result of adjustments to net assets acquired as reductions of goodwill when the escrows are settled. The maximum potential earnout payables disclosed in the foregoing table represent the maximum amount of additional consideration that could be paid pursuant to the terms of the purchase agreement for the applicable acquisition. The amounts recorded as earnout payables, which are primarily based upon the estimated future operating results of the acquired entities over a two- to three-year period subsequent to the acquisition date, are measured at fair value as of the acquisition date and are included on that basis in the recorded purchase price consideration in the foregoing table. The $48.2 million accrued liability related to Ashton Tiffany in the foregoing table may be settled using shares of our common stock in early February 2021. We will record subsequent changes in these estimated earnout obligations, including the accretion of discount, in our consolidated statement of earnings when incurred. The fair value of these earnout obligations is based on the present value of the expected future payments to be made to the sellers of the acquired entities in accordance with the provisions outlined in the respective purchase agreements, which is a Level 3 fair value measurement. In determining fair value, we estimated the acquired entity’s future performance using financial projections developed by management for the acquired entity and market participant assumptions that were derived for revenue growth and/or profitability. Revenue growth rates generally ranged from 2.5% to 15.0% for our 2020 acquisitions. We estimated future payments using the earnout formula and performance targets specified in each purchase agreement and the financial projections just described. We then discounted these payments to present value using a risk-adjusted rate that takes into consideration market‑based rates of return that reflect the ability of the acquired entity to achieve the targets. The discount rates generally ranged from 6.0% to 9.0% for our 2020 acquisitions. Changes in financial projections, market participant assumptions for revenue growth and/or profitability, or the risk-adjusted discount rate, would result in a change in the fair value of recorded earnout obligations. During 2020, 2019 and 2018, we recognized $32.5 million, $27.0 million and $18.8 million, respectively, of expense in our consolidated statement of earnings related to the accretion of the discount recorded for earnout obligations in connection with our acquisitions. In addition, during 2020, 2019 and 2018, we recognized $65.4 million, $11.7 million and $9.2 million of income, respectively, related to net adjustments in the estimated fair value of the liability for earnout obligations in connection with revised projections of future performance for 135, 116 and 112 acquisitions, respectively. The aggregate amount of maximum earnout obligations related to acquisitions made in 2017 and subsequent years was $1,128.1 million as of December 31, 2020, of which $592.2 million was recorded in the consolidated balance sheet as of that date based on the estimated fair value of the expected future payments to be made, of which approximately $493.7 million can be settled in cash or stock at our option and $98.5 million must be settled in cash. The aggregate amount of maximum earnout obligations related to acquisitions made in 2016 and subsequent years was $982.9 million as of December 31, 2019, of which $565.0 million was recorded in the consolidated balance sheet as of that date based on the estimated fair value of the expected future payments to be made. The following is a summary of the estimated fair values of the net assets acquired at the date of each acquisition made in 2020 (in millions): CRB HES CRES OTI CIA HAI AT Twenty Other Acquisitions Total Cash and restricted cash $ - $ 3.3 $ 4.3 $ 0.6 $ 4.2 $ 2.3 $ 6.0 $ 13.3 $ 34.0 Other current assets - 1.0 12.4 3.0 28.8 9.0 8.6 25.2 88.0 Fixed assets - - - 0.9 0.1 1.1 0.5 0.6 3.2 Noncurrent assets 7.6 0.8 - 6.7 0.9 6.4 2.1 3.1 27.6 Goodwill 108.4 19.1 21.3 25.4 58.9 45.7 14.8 66.0 359.6 Expiration lists 133.7 13.7 13.9 18.3 56.2 62.5 78.2 90.7 467.2 Non-compete agreements 2.9 0.1 - 0.4 0.8 0.7 5.8 0.7 11.4 Trade names 4.7 - 0.3 - 7.5 - - - 12.5 Total assets acquired 257.3 38.0 52.2 55.3 157.4 127.7 116.0 199.6 1,003.5 Current liabilities - 4.4 15.7 5.2 28.1 9.5 8.4 32.3 103.6 Noncurrent liabilities - 0.5 - 7.5 0.2 6.4 2.1 7.1 23.8 Total liabilities assumed - 4.9 15.7 12.7 28.3 15.9 10.5 39.4 127.4 Total net assets acquired $ 257.3 $ 33.1 $ 36.5 $ 42.6 $ 129.1 $ 111.8 $ 105.5 $ 160.2 $ 876.1 Among other things, these acquisitions allow us to expand into desirable geographic locations, further extend our presence in the retail and wholesale insurance and Provisional estimates of fair value are established at the time of each acquisition and are subsequently reviewed within the first year of operations subsequent to the acquisition date to determine the necessity for adjustments. Fair value estimates were provisional for some of the 2020 acquisitions as of December 31, 2020. Fair value adjustments, if any, are most common to the values established for amortizable intangible assets and earnout liabilities, with the offset to goodwill. The fair value of the tangible assets and liabilities for each applicable acquisition at the acquisition date approximated their carrying values. The fair value of expiration lists was established using the excess earnings method, which is an income approach based on estimated financial projections developed by management for each acquired entity using market participant assumptions. Revenue growth and attrition rates generally ranged from 1.5% based on a risk-adjusted rate that takes into consideration market-based rates of return and reflects the risk of the asset relative to the acquired business. These discount rates generally ranged from 9.0 % to 13.5 % for our 2020 and 2019 acquisitions, for which valuation s were performed in 2020 . The fair value of non-compete agreements was established using the profit differential method, which is an income approach based on estimated financial projections developed by management for the acquired company using market participant assumptions and various non-compete scenarios. Expiration lists, non-compete agreements and trade names related to our acquisitions are amortized using the straight-line method over their estimated useful lives (two to fifteen years for expiration lists, two to six years for non-compete agreements and two to fifteen years for trade names), while goodwill is not subject to amortization. We use the straight-line method to amortize these intangible assets because the pattern of their economic benefits cannot be reasonably determined with any certainty. We review all of our identifiable intangible assets for impairment periodically (at least annually) and whenever events or changes in business circumstances indicate that the carrying value of the assets may not be recoverable. In reviewing identifiable intangible assets, if the undiscounted future cash flows were less than the carrying amount of the respective (or underlying) asset, an indicator of impairment would exist and further analysis would be required to determine whether or not a loss would need to be charged against current period earnings as a component of amortization expense. Based on the results of impairment reviews in 2020, 2019 and 2018, we wrote off $51.7 million, $0.1 million and $10.6 million, respectively, of amortizable intangible assets related to the brokerage and risk management segments. Of the $467.2 million of expiration lists, $11.4 million of non-compete agreements and $12.5 million of trade names related to the 2020 acquisitions, $29.0 million, $0.6 million and zero, respectively, is not expected to be deductible for income tax purposes. Accordingly, we recorded a deferred tax liability of $3.9 million, and a corresponding amount of goodwill, in 2020 related to the nondeductible amortizable intangible assets. Our consolidated financial statements for the year ended December 31, 2020 include the operations of the acquired entities from their respective acquisition dates. The following is a summary of the unaudited pro forma historical results, as if these entities had been acquired at January 1, 2019 (in millions, except per share data): Year Ended December 31, 2020 2019 Total revenues $ 7,108.7 $ 7,352.7 Net earnings attributable to controlling interests 817.6 670.5 Basic net earnings per share 4.26 3.57 Diluted net earnings per share 4.17 3.49 The unaudited pro forma results above have been prepared for comparative purposes only and do not purport to be indicative of the results of operations which actually would have resulted had these acquisitions occurred at January 1, 2019, nor are they necessarily indicative of future operating results. Annualized revenues of entities acquired in 2020 totaled approximately $251.4 million. Total revenues and net earnings recorded in our consolidated statement of earnings for 2020 related to the 2020 acquisitions in the aggregate, were $52.7 million and $5.2 million, respectively.

Contracts with Customers

Contracts with Customers	12 Months Ended
Contracts with Customers	Dec. 31, 2020
Revenue From Contract With Customer [Abstract]
Contracts with Customers	4. Contracts with Customers Contract Assets and Liabilities/Contract Balances Information about unbilled receivables, contract assets and contract liabilities from contracts with customers is as follows (in millions): December 31, 2020 December 31, 2019 Unbilled receivables $ 603.1 $ 556.4 Deferred contract costs 102.0 98.3 Deferred revenue 541.3 503.8 The unbilled receivables, which are included in premium and fees receivable in our consolidated balance sheet, primarily relate to our rights to consideration for work completed but not billed at the reporting date. These are transferred to the receivables when the client is billed. The deferred contract costs represent the costs we incur to fulfill a new or renewal contract with our clients prior to the effective date of the contract. These costs are expensed on the contract effective date. The deferred revenue in the consolidated balance sheet included amounts that represent the remaining performance obligations under our contracts and amounts collected related to advanced billings and deposits received from customers that may or may not ultimately be recognized as revenues in the future. Deposits received from customers could be returned to the customers based on lesser actual transactional volume than originally billed volume. Significant changes in the deferred revenue balances, which include foreign currency translation adjustments, during the period are as follows (in millions): Brokerage Risk Management Total Deferred revenue at December 31, 2018 $ 284.7 $ 173.0 $ 457.7 Incremental deferred revenue 254.7 109.6 364.3 Revenue recognized during the year ended December 31, 2019 included in deferred revenue at December 31, 2018 (227.5 ) (122.0 ) (349.5 ) Net change in collected billings/deposits received from customers (6.7 ) 5.6 (1.1 ) Impact of changes in foreign exchange rates 1.4 0.4 1.8 Deferred revenue recognized from business acquisitions 30.6 — 30.6 Deferred revenue at December 31, 2019 337.2 166.6 503.8 Incremental deferred revenue 282.7 91.3 374.0 Revenue recognized during the year ended December 31, 2020 included in deferred revenue at December 31, 2019 (283.1 ) (99.2 ) (382.3 ) Net change in collected billings/deposits received from customers (0.7 ) 26.3 25.6 Impact of changes in foreign exchange rates 8.7 1.6 10.3 Deferred revenue recognized from business acquisitions 9.9 — 9.9 Deferred revenue at December 31, 2020 $ 354.7 $ 186.6 $ 541.3 Revenue recognized during 2020 in the table above included revenue from 2019 acquisitions that would not be reflected in prior years. Remaining Performance Obligations Remaining performance obligations represent the portion of the contract price for which work has not been performed. As of December 31, 2020, the aggregate amount of the contract price allocated to remaining performance obligations was $541.3 million. The estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied (or partially unsatisfied) at the end of the reporting period is as follows (in millions): Brokerage Risk Management Total 2021 $ 328.4 $ 122.8 $ 451.2 2022 23.6 31.2 54.8 2023 1.4 14.2 15.6 2024 0.6 6.5 7.1 2025 0.4 4.0 4.4 Thereafter 0.3 7.9 8.2 Total $ 354.7 $ 186.6 $ 541.3 Deferred Contract Costs We capitalize costs incurred to fulfill contracts as “deferred contract costs” which are included in other current assets in our consolidated balance sheet. Deferred contract costs were $102.0 million and $98.3 million as of December 31, 2020 and 2019, respectively. Capitalized fulfillment costs are amortized to expense on the contract effective date. The amount of amortization of the deferred contract costs was $388.4 million and $355.9 million for the years ended December 31, 2020 and 2019, respectively. We have applied the practical expedient to recognize the incremental costs of obtaining contracts as an expense when incurred if the amortization period of the assets that we otherwise would have recognized is one year or less for our brokerage segment. These costs are included in compensation and operating expenses in our consolidated statement of earnings.

Other Financial Data

Other Financial Data	12 Months Ended
Other Financial Data	Dec. 31, 2020
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Other Financial Data	5. Other Financial Data Other Current Assets Major classes of other current assets consist of the following (in millions): December 31, 2020 2019 Premium finance advances and loans $ 442.7 $ 388.1 Accrued supplemental, direct bill and other receivables 361.7 369.1 Refined coal production related receivables 95.4 103.4 Deferred contract costs 102.0 98.3 Prepaid expenses 112.1 115.5 Total other current assets $ 1,113.9 $ 1,074.4 The premium finance advances and loans represent short-term loans which we make to many of our brokerage related clients and other non‑brokerage clients to finance their premiums paid to underwriting enterprises

Fixed Assets

Fixed Assets	12 Months Ended
Fixed Assets	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Fixed Assets	6. Fixed Assets Major classes of fixed assets consist of the following (in millions): December 31, 2020 2019 Office equipment $ 33.0 $ 32.6 Furniture and fixtures 138.3 126.0 Leasehold improvements 166.0 150.2 Computer equipment 214.2 176.3 Land and buildings - corporate headquarters 145.1 144.9 Software 452.2 392.3 Other 16.7 19.0 Work in process 14.1 18.0 1,179.6 1,059.3 Accumulated depreciation (728.9 ) (591.9 ) Net fixed assets $ 450.7 $ 467.4 The amounts in work in process in the table above primarily are for capitalized expenditures incurred related to IT development projects in 2020 and 2019.

Intangible Assets

Intangible Assets	12 Months Ended
Intangible Assets	Dec. 31, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Intangible Assets	7. Intangible Assets The carrying amount of goodwill at December 31, 2020 and 2019 allocated by domestic and foreign operations is as follows (in millions): Brokerage Risk Management Corporate Total At December 31, 2020 United States $ 3,399.8 $ 33.2 $ - $ 3,433.0 United Kingdom 1,328.3 15.1 - 1,343.4 Canada 492.9 - - 492.9 Australia 462.1 11.5 - 473.6 New Zealand 221.9 10.7 - 232.6 Other foreign 148.6 - 2.9 151.5 Total goodwill - net $ 6,053.6 $ 70.5 $ 2.9 $ 6,127.0 At December 31, 2019 United States 3,163.8 33.1 - 3,196.9 United Kingdom 1,177.8 12.9 - 1,190.7 Canada 454.4 - - 454.4 Australia 416.5 10.5 - 427.0 New Zealand 208.0 10.1 - 218.1 Other foreign 128.4 - 3.0 131.4 Total goodwill - net $ 5,548.9 $ 66.6 $ 3.0 $ 5,618.5 The changes in the carrying amount of goodwill for 2020 and 2019 are as follows (in millions): Brokerage Risk Management Corporate Total Balance as of December 31, 2018 $ 4,573.6 $ 49.3 $ 2.7 $ 4,625.6 Goodwill acquired during the year 958.4 16.9 0.4 975.7 Goodwill adjustments related to appraisals and other acquisition adjustments 0.2 (0.2 ) - - Goodwill written-off related to sales of business (7.2 ) - - (7.2 ) Foreign currency translation adjustments during the year 23.9 0.6 (0.1 ) 24.4 Balance as of December 31, 2019 5,548.9 66.6 3.0 5,618.5 Goodwill acquired during the year 359.6 - - 359.6 Goodwill adjustments related to appraisals and other acquisition adjustments 29.8 1.7 - 31.5 Foreign currency translation adjustments during the year 115.3 2.2 (0.1 ) 117.4 Balance as of December 31, 2020 $ 6,053.6 $ 70.5 $ 2.9 $ 6,127.0 Major classes of amortizable intangible assets consist of the following (in millions): December 31, 2020 2019 Expiration lists $ 4,753.2 $ 4,246.0 Accumulated amortization - expiration lists (2,436.7 ) (2,004.3 ) 2,316.5 2,241.7 Non-compete agreements 75.9 68.4 Accumulated amortization - non-compete agreements (57.8 ) (52.5 ) 18.1 15.9 Trade names 107.8 91.8 Accumulated amortization - trade names (42.5 ) (30.7 ) 65.3 61.1 Net amortizable assets $ 2,399.9 $ 2,318.7 Estimated aggregate amortization expense for each of the next five years is as follows (in millions): 2021 $ 378.4 2022 352.3 2023 327.1 2024 291.3 2025 251.3 Thereafter 799.5 Total $ 2,399.9

Credit and Other Debt Agreement

Credit and Other Debt Agreements	12 Months Ended
Credit and Other Debt Agreements	Dec. 31, 2020
Debt Disclosure [Abstract]
Credit and Other Debt Agreements	8. Credit and Other Debt Agreements The following is a summary of our corporate and other debt (in millions): December 31, 2020 2019 Note Purchase Agreements: Semi-annual payments of interest, fixed rate of 3.48%, balloon due June 24, 2020 $ - $ 50.0 Semi-annual payments of interest, fixed rate of 3.99%, balloon due July 10, 2020 - 50.0 Semi-annual payments of interest, fixed rate of 5.18%, balloon due February 10, 2021 75.0 75.0 Semi-annual payments of interest, fixed rate of 3.69%, balloon due June 14, 2022 200.0 200.0 Semi-annual payments of interest, fixed rate of 5.49%, balloon due February 10, 2023 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.13%, balloon due June 24, 2023 200.0 200.0 Quarterly payments of interest, floating rate of 90 day LIBOR plus 1.65%, balloon due August 2, 2023 (prepaid on November 3, 2020) - 50.0 Semi-annual payments of interest, fixed rate of 4.72%, balloon due February 13, 2024 100.0 100.0 Semi-annual payments of interest, fixed rate of 4.58%, balloon due February 27, 2024 325.0 325.0 Quarterly payments of interest, floating rate of 90 day LIBOR plus 1.40%, balloon due June 13, 2024 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.31%, balloon due June 24, 2025 200.0 200.0 Semi-annual payments of interest, fixed rate of 4.85%, balloon due February 13, 2026 140.0 140.0 Semi-annual payments of interest, fixed rate of 4.73%, balloon due February 27, 2026 175.0 175.0 Semi-annual payments of interest, fixed rate of 4.40%, balloon due June 2, 2026 175.0 175.0 Semi-annual payments of interest, fixed rate of 4.36%, balloon due June 24, 2026 150.0 150.0 Semi-annual payments of interest, fixed rate of 3.75%, balloon due January 30, 2027 30.0 - Semi-annual payments of interest, fixed rate of 4.09%, balloon due June 27, 2027 125.0 125.0 Semi-annual payments of interest, fixed rate of 4.09%, balloon due August 2, 2027 125.0 125.0 Semi-annual payments of interest, fixed rate of 4.14%, balloon due August 4, 2027 98.0 98.0 Semi-annual payments of interest, fixed rate of 3.46%, balloon due December 1, 2027 100.0 100.0 Semi-annual payments of interest, fixed rate of 4.55%, balloon due June 2, 2028 75.0 75.0 Semi-annual payments of interest, fixed rate of 4.34%, balloon due June 13, 2028 125.0 125.0 Semi-annual payments of interest, fixed rate of 5.04%, balloon due February 13, 2029 100.0 100.0 Semi-annual payments of interest, fixed rate of 4.98%, balloon due February 27, 2029 100.0 100.0 Semi-annual payments of interest, fixed rate of 4.19%, balloon due June 27, 2029 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.19%, balloon due August 2, 2029 50.0 50.0 Semi-annual payments of interest, fixed rate of 3.48%, balloon due December 2, 2029 50.0 50.0 Semi-annual payments of interest, fixed rate of 3.99%, balloon due January 30, 2030 341.0 - Semi-annual payments of interest, fixed rate of 4.44%, balloon due June 13, 2030 125.0 125.0 Semi-annual payments of interest, fixed rate of 5.14%, balloon due March 13, 2031 180.0 180.0 Semi-annual payments of interest, fixed rate of 4.70%, balloon due June 2, 2031 25.0 25.0 Semi-annual payments of interest, fixed rate of 4.09%, balloon due January 30, 2032 69.0 - Semi-annual payments of interest, fixed rate of 4.34%, balloon due June 27, 2032 75.0 75.0 Semi-annual payments of interest, fixed rate of 4.34%, balloon due August 2, 2032 75.0 75.0 Semi-annual payments of interest, fixed rate of 4.59%, balloon due June 13, 2033 125.0 125.0 Semi-annual payments of interest, fixed rate of 5.29%, balloon due March 13, 2034 40.0 40.0 Semi-annual payments of interest, fixed rate of 4.48%, balloon due June 12, 2034 175.0 175.0 Semi-annual payments of interest, fixed rate of 4.24%, balloon due January 30, 2035 79.0 - Semi-annual payments of interest, fixed rate of 4.69%, balloon due June 13, 2038 75.0 75.0 Semi-annual payments of interest, fixed rate of 5.45%, balloon due March 13, 2039 40.0 40.0 Semi-annual payments of interest, fixed rate of 4.49%, balloon due January 30, 2040 56.0 - Total Note Purchase Agreements 4,348.0 3,923.0 Credit Agreement: Periodic payments of interest and principal, prime or LIBOR plus up to 1.45%, expires June 7, 2024 - 520.0 Premium Financing Debt Facility - expires September 15, 2022: Facility B AUD denominated tranche, interbank rates plus 1.400% 193.1 142.1 NZD denominated tranche, interbank rates plus 1.750% - - Facility C and D AUD denominated tranche, interbank rates plus 0.730% - 18.8 NZD denominated tranche, interbank rates plus 0.940% 10.5 9.7 Total Premium Financing Debt Facility 203.6 170.6 Total corporate and other debt 4,551.6 4,613.6 Less unamortized debt acquisition costs on Note Purchase Agreements (7.0 ) (6.9 ) Net corporate and other debt $ 4,544.6 $ 4,606.7 Note Purchase Agreements - On February 13, 2019, we closed an offering of $600.0 million aggregate principal amount of fixed rate private placement senior unsecured notes. This offering was funded on February 13, 2019 ($340.0 million) and March 13, 2019 ($260.0 million). The weighted average maturity of these notes is 10.1 years and the weighted average interest rate is 5.04% after giving effect to a net hedging loss. In 2017 and 2018, we entered into pre-issuance interest rate hedging transactions related to this private placement. We realized a net cash loss of approximately $1.2 million on the hedging transactions that will be recognized on a pro rata basis as an increase in our reported interest expense over the life of the debt. We used the proceeds of this offering to repay certain existing indebtedness and fund acquisitions. The notes consist of the following tranches: • $100.0 million of 4.72% senior notes due in 2024; • $140.0 million of 4.85% senior notes due in 2026 • $100.0 million of 5.04% senior notes due in 2029 • $180.0 million of 5.14% senior notes due in 2031 • $40.0 million of 5.29% senior notes due in 2034 • $40.0 million of 5.45% senior notes due in 2039 On June 12, 2019, we closed a private placement of $175.0 million aggregate principal amount of unsecured senior notes. The unsecured senior notes were issued with an interest rate of 4.48% and are due in 2034. We used the proceeds of these offerings in part to fund the $50.0 million June 24, 2019 Series L note maturity, and for acquisitions and general corporate purposes. The weighted average interest rate is 4.68% after giving effect to a net hedging loss. In 2017 and 2018, we entered into pre-issuance interest rate hedging transactions related to this private placement. We realized a net cash loss of approximately $5.2 million on the hedging transactions that will be recognized on a pro rata basis as an increase in our reported interest expense over ten years of the total 15‑year notes. On December 2, 2019 we closed a private placement of $50.0 million aggregate principal amount of unsecured senior notes. The unsecured senior notes were issued with an interest rate and weighted average interest rate of 3.48% and are due in 2029. We used the proceeds of those offerings to fund the $50.0 million November 30, 2019 Series C note maturity. On January 30, 2020, we closed and funded an offering of $575.0 million aggregate principal amount of fixed rate private placement unsecured senior notes. The weighted average maturity of these notes is 11.7 years and the weighted average interest rate is 4.23% per annum after giving effect to underwriting costs and the net hedge loss. In 2017 and 2018, we entered into pre-issuance interest rate hedging transactions related to this private placements. We realized a net cash loss of approximately $8.9 million on the hedging transactions that will be recognized on a pro rata basis as an increase to our reported interest expense over a ten year period. The notes consist of the following tranches: • $30.0 million of 3.75% senior notes due in 2027 • $341.0 million of 3.99% senior notes due in 2030 • $69.0 million of 4.09% senior notes due in 2032 • $79.0 million of 4.24% senior notes due in 2035 • $56.0 million of 4.49% senior notes due in 2040 We used these offerings to repay certain existing indebtedness and for general corporate purposes, including to fund acquisitions. Under the terms of the note purchase agreements described above, we may redeem the notes at any time, in whole or in part, at 100% of the principal amount of such notes being redeemed, together with accrued and unpaid interest and a “make-whole amount”. The “make-whole amount” is derived from a net present value computation of the remaining scheduled payments of principal and interest using a discount rate based on the U.S. Treasury yield plus 0.5% and is designed to compensate the purchasers of the notes for their investment risk in the event prevailing interest rates at the time of prepayment are less favorable than the interest rates under the notes. We do not currently intend to prepay any of the notes. The note purchase agreements described above contain customary provisions for transactions of this type, including representations and warranties regarding us and our subsidiaries and various financial covenants, including covenants that require us to maintain specified financial ratios. We were in compliance with these covenants as of December 31, 2020. The note purchase agreements also provide customary events of default, generally with corresponding grace periods, including, without limitation, payment defaults with respect to the notes, covenant defaults, cross-defaults to other agreements evidencing our or our subsidiaries’ indebtedness, certain judgments against us or our subsidiaries and events of bankruptcy involving us or our material subsidiaries. The notes issued under the note purchase agreement are senior unsecured obligations of ours and rank equal in right of payment with our Credit Agreement discussed below. Credit Agreement - On June 7, 2019, we entered into an amendment and restatement to our multicurrency credit agreement dated April 8, 2016, (which we refer to as the Credit Agreement) with a group of fifteen financial institutions. The amendment and restatement, among other things, extended the expiration date of the Credit Agreement from April 8, 2021 to June 7, 2024 and increased the revolving credit commitment from $800.0 million to $1,200.0 million, of which up to $75.0 million may be used for issuances of standby or commercial letters of credit and up to $75.0 million may be used for the making of swing loans (as defined in the Credit Agreement). We may from time to time request, subject to certain conditions, an increase in the revolving credit commitment under the Credit Agreement up to a maximum aggregate revolving credit commitment of $1,700.0 million. On August 27, 2020, we entered into an amendment to the Credit Agreement providing that the obligations of each subsidiary of Gallagher that was a borrower, guarantor and/or obligor under the Credit Agreement, ceased to apply and that each subsidiary was released from all of its obligations under the Credit Agreement. The amendment also replaced the minimum asset covenant with a priority indebtedness covenant, substantially similar to other priority indebtedness covenants applicable to us under our private placement note purchase agreements. The Credit Agreement provides that we may elect that each borrowing in U.S. dollars be either base rate loans or eurocurrency loans, each as defined in the Credit Agreement. However, the Credit Agreement provides that all loans denominated in currencies other than U.S. dollars will be eurocurrency loans. Interest rates on base rate loans and outstanding drawings on letters of credit in U.S. dollars under the Credit Agreement will be based on the base rate, as defined in the Credit Agreement, plus a margin of 0.00% to 0.45%, depending on the financial leverage ratio we maintain. Interest rates on eurocurrency loans or outstanding drawings on letters of credit in currencies other than U.S. dollars under the Credit Agreement will be based on adjusted LIBOR, as defined in the Credit Agreement, plus a margin of 0.85% to 1.45%, depending on the financial leverage ratio we maintain. Interest rates on swing loans will be based, at our election, on either the base rate or an alternate rate that may be quoted by the lead lender. The annual facility fee related to the Credit Agreement is 0.15% and 0.30% of the revolving credit commitment, depending on the financial leverage ratio we maintain. In connection with entering into the Credit Agreement, we incurred approximately $2.5 million of debt acquisition costs that were capitalized and will be amortized on a pro rata basis over the term of the Credit Agreement. The terms of the Credit Agreement include various financial covenants, including covenants that require us to maintain specified financial ratios. We were in compliance with these covenants as of December 31, 2020. The Credit Agreement also includes customary provisions for transactions of this type, including events of default, with corresponding grace periods and cross‑defaults to other agreements evidencing our indebtedness. At December 31, 2020, $17.4 million of letters of credit (for which we had $17.5 million of liabilities recorded at December 31, 2020) were outstanding under the Credit Agreement. See Note 17 to these consolidated financial statements for a discussion of the letters of credit. There were no borrowings outstanding under the Credit Agreement at December 31, 2020. Accordingly, at December 31, 2020, $1,182.6 million remained available for potential borrowings. Premium Financing Debt Facility - On September 16, 2020, we entered into an amendment to our revolving loan facility (which we refer to as the Premium Financing Debt Facility), that provides funding for the three Australian (AU) and New Zealand (NZ) premium finance subsidiaries. The amendment, among other things, extended the expiration date of the Premium Financing Debt Facility from July 18, 2021 to September 15, 2022, added six-months variable limits to Facility B NZ$ beginning in 2021 and increased the total commitment for the AU$ denominated tranche from AU$245.0 million to AU$310.0 million. The Premium Financing Debt Facility is comprised of: (i) Facility B is separated into AU$260.0 million and NZ$25.0 million tranches, (ii) Facility C, an AU$50.0 million equivalent multi-currency overdraft tranche and (iii) Facility D, a NZ$15.0 million equivalent multi-currency overdraft tranche. The interest rates on Facility B are Interbank rates, which vary by tranche, duration and currency, plus a margin of 1.400% and 1.750% for the AU$ and NZ$ tranches, respectively. The interest rates on Facilities C and D are 30 day Interbank rates, plus a margin of 0.730% and 0.940% for the AU$ and NZ$ tranches, respectively. The annual fee for Facility B is 0.63% and 0.7875% for the undrawn commitments for the AU$ and NZ$ tranches, respectively. The annual fee for Facility C is 0.67% and for Facility D is 0.86% of the total commitments of the facilities. The terms of our Premium Financing Debt Facility include various financial covenants, including covenants that require us to maintain specified financial ratios. We were in compliance with these covenants as of December 31, 2020. The Premium Financing Debt Facility also includes customary provisions for transactions of this type, including events of default, with corresponding grace periods and cross-defaults to other agreements evidencing our indebtedness. Facilities B, C and D are secured by the premium finance receivables of the Australian and New Zealand premium finance subsidiaries. At December 31, 2020, AU$255.0 million and NZ$0.0 of borrowings were outstanding under Facility B, AU$0.0 million of borrowings outstanding under Facility C and NZ$14.9 million of borrowings were outstanding under Facility D, which in aggregate amount to US$203.6 million of borrowings under the Premium Finance Debt Facility. Accordingly, as of December 31, 2020, AU$5.0 and NZ$25.0 million remained available for potential borrowing under Facility B, and AU$50.0 million and NZ$0.1 million under Facilities C and D, respectively. See Note 17 to these 2020 consolidated financial statements for additional discussion on our contractual obligations and commitments as of December 31, 2020. The aggregate estimated fair value of the $4,348.0 million in debt under the note purchase agreements at December 31, 2020 was $5,018.9 million due to the long-term duration and fixed interest rates associated with these debt obligations. No active or observable market exists for our private long-term debt. Therefore, the estimated fair value of this debt is based on the income valuation approach, which is a valuation technique that converts future amounts (for example, cash flows or income and expenses) to a single current (that is, discounted) amount. The fair value measurement is determined on the basis of the value indicated by current market expectations about those future amounts. Because our debt issuances generate a measurable income stream for each lender, the income approach was deemed to be an appropriate methodology for valuing the private placement long-term debt. The methodology used calculated the original deal spread at the time of each debt issuance, which was equal to the difference between the yield of each issuance (the coupon rate) and the equivalent benchmark treasury yield at that time. The market spread as of the valuation date was calculated, which is equal to the difference between an index for investment grade insurers and the equivalent benchmark treasury yield today. An implied premium or discount to the par value of each debt issuance based on the difference between the origination deal spread and market as of the valuation date was then calculated. The index we relied on to represent investment graded insurers was the Bloomberg Valuation Services (BVAL) U.S. Insurers BBB index. This index is comprised primarily of insurance brokerage firms and was representative of the industry in which we operate. For the purpose of our analysis, the average BBB rate was assumed to be the appropriate borrowing rate for us. The estimated fair value of the zero of borrowings outstanding under our Credit Agreement approximate their carrying value due to their short-term duration and variable interest rates. The estimated fair value of the $203.6 million of borrowings outstanding under our Premium Financing Debt Facility approximates their carrying value due to their short-term duration and variable interest rates.

Earnings per Share

Earnings per Share	12 Months Ended
Earnings per Share	Dec. 31, 2020
Earnings Per Share [Abstract]
Earnings per Share	9. Earnings per Share The following table sets forth the computation of basic and diluted net earnings per share (in millions, except per share data): Year Ended December 31, 2020 2019 2018 Net earnings attributable to controlling interests $ 818.8 $ 668.8 $ 633.5 Weighted average number of common shares outstanding 191.0 186.0 182.7 Dilutive effect of stock options using the treasury stock method 4.0 4.1 3.5 Weighted average number of common and common equivalent shares outstanding 195.0 190.1 186.2 Basic net earnings per share $ 4.29 $ 3.60 $ 3.47 Diluted net earnings per share $ 4.20 $ 3.52 $ 3.40 There were no anti-dilutive stock-based awards outstanding at December 31, 2020 that were excluded in the computation of the dilutive effect of stock-based awards for the year then ended. Anti-dilutive stock-based awards of 1.0 million and 1.0 million shares were outstanding at December 31, 2019 and 2018, respectively, but were excluded in the computation of the dilutive effect of stock‑based awards for the year then ended. These stock-based awards were excluded from the computation because the exercise prices on these stock-based awards were greater than the average market price of our common shares during the respective period, and therefore, would be anti-dilutive to earnings per share under the treasury stock method.

Stock Option Plans

Stock Option Plans	12 Months Ended
Stock Option Plans	Dec. 31, 2020
Text Block [Abstract]
Stock Option Plans	10. Stock Option Plans On May 16, 2017, our stockholders approved the Arthur J. Gallagher & Co. 2017 Long-Term Incentive Plan (which we refer to as the LTIP), which replaced our previous stockholder-approved Arthur J. Gallagher & Co. 2014 Long-Term Incentive Plan (which we refer to as the 2014 LTIP). The LTIP term began May 16, 2017 and terminates on the date of the annual meeting of stockholders in 2027, unless terminated earlier by our board of directors. All of our officers, employees and non-employee directors are eligible to receive awards under the LTIP. The compensation committee of our board of directors determines the annual number of shares delivered under the LTIP. The LTIP provides for non-qualified and incentive stock options, stock appreciation rights, restricted stock and restricted stock units, any or all of which may be made contingent upon the achievement of performance criteria. Shares of our common stock available for issuance under the LTIP include authorized and unissued shares of common stock or authorized and issued shares of common stock reacquired and held as treasury shares or otherwise, or a combination thereof. The number of available shares will be reduced by the aggregate number of shares that become subject to outstanding awards granted under the LTIP. To the extent that shares subject to an outstanding award granted under either the LTIP or prior equity plans are not issued or delivered by reason of the expiration, termination, cancellation or forfeiture of such award or by reason of the settlement of such award in cash, then such shares will again be available for grant under the LTIP. The maximum number of shares available under the LTIP for restricted stock, restricted stock unit awards and performance unit awards settled with stock (i.e., all awards other than stock options and stock appreciation rights) is 2.3 million as of December 31, 2020. The LTIP provides for the grant of stock options, which may be either tax-qualified incentive stock options or non-qualified options and stock appreciation rights. The compensation committee determines the period for the exercise of a non-qualified stock option, tax-qualified incentive stock option or stock appreciation right, provided that no option can be exercised later than seven years after its date of grant. The exercise price of a non-qualified stock option or tax-qualified incentive stock option and the base price of a stock appreciation right cannot be less than 100% of the fair market value of a share of our common stock on the date of grant, provided that the base price of a stock appreciation right granted in tandem with an option will be the exercise price of the related option. Upon exercise, the option exercise price may be paid in cash, by the delivery of previously owned shares of our common stock, through a net-exercise arrangement, or through a broker-assisted cashless exercise arrangement. The compensation committee determines all of the terms relating to the exercise, cancellation or other disposition of an option or stock appreciation right upon a termination of employment, whether by reason of disability, retirement, death or any other reason. Stock option and stock appreciation right awards under the LTIP are non-transferable. On March 12, 2020, the compensation committee granted 1,590,740 options under the 2017 LTIP to our officers and key employees that become exercisable at the rate of 34%, 33% and 33% on the anniversary date of the grant in 2023, 2024 and 2025, respectively. On March 14, 2019, the compensation committee granted 1,283,300 options under the 2017 LTIP to our officers and key employees that become exercisable at the rate of 34%, 33% and 33% on the anniversary date of the grant in 2022, 2023 and 2024, respectively. On March 15, 2018, the compensation committee granted 1,261,000 options under the 2017 LTIP to our officers and key employees that become exercisable at the rate of 34%, 33% and 33% on the anniversary date of the grant in 2021, 2022 and 2023, respectively. The 2020, 2019 and 2018 options expire seven years from the date of grant, or earlier in the event of certain terminations of employment. For our executive officers age 55 or older, stock options awarded in 2020, 2019 and 2018 are not subject to forfeiture upon such officers’ departure from the company after two years from the date of grant. Our stock option plans provide for the immediate vesting of all outstanding stock option grants in the event of a change in control of our company, as defined in the applicable plan documents. During 2020, 2019 and 2018, we recognized $13.6 million, $14.0 million and $13.7 million, respectively, of compensation expense related to our stock option grants. For purposes of expense recognition in 2020, 2019 and 2018, the estimated fair values of the stock option grants are amortized to expense over the options’ vesting period. We estimated the fair value of stock options at the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions: Year Ended December 31, 2020 2019 2018 Expected dividend yield 2.1 % 1.7 % 2.3 % Expected risk-free interest rate 0.7 % 2.5 % 2.7 % Volatility 17.3 % 15.6 % 15.1 % Expected life (in years) 5.4 5.5 5.5 Option valuation models require the input of highly subjective assumptions including the expected stock price volatility. The Black-Scholes option pricing model was developed for use in estimating the fair value of traded options which have no vesting restrictions and are fully transferable. The weighted average fair value per option for all options granted during 2020, 2019 and 2018, as determined on the grant date using the Black-Scholes option pricing model, was $9.99, $10.71 and $9.27, respectively. The following is a summary of our stock option activity and related information for 2020 and 2019 (in millions, except exercise price and year data): Weighted Average Weighted Remaining Shares Average Contractual Aggregate Under Exercise Term Intrinsic Option Price (in years) Value Year Ended December 31, 2020 Beginning balance 7.9 $ 56.40 Granted 1.6 86.17 Exercised (1.8 ) 45.80 Forfeited or canceled (0.2 ) 65.87 Ending balance 7.5 $ 65.09 3.86 $ 437.9 Exercisable at end of year 1.9 $ 47.17 1.83 $ 147.2 Ending unvested and expected to vest 5.3 $ 70.74 4.51 $ 278.1 Year Ended December 31, 2019 Beginning balance 8.8 $ 50.16 Granted 1.3 79.59 Exercised (1.9 ) 42.91 Forfeited or canceled (0.3 ) 57.33 Ending balance 7.9 $ 56.40 3.75 $ 308.6 Exercisable at end of year 2.0 $ 45.03 1.82 $ 101.9 Ending unvested and expected to vest 5.7 $ 59.76 4.36 $ 201.5 Options with respect to 11.4 million shares (less any shares of restricted stock issued under the LTIP - see Note 12 to these consolidated financial statements) were available for grant under the LTIP at December 31, 2020. The total intrinsic value of options exercised during 2020, 2019 and 2018 amounted to $106.4 million, $77.9 million and $54.2 million, respectively. As of December 31, 2020, we had approximately $28.3 million of total unrecognized compensation expense related to nonvested options. We expect to recognize that cost over a weighted average period of approximately four years. Other information regarding stock options outstanding and exercisable at December 31, 2020 is summarized as follows (in millions, except exercise price and year data): Options Outstanding Options Exercisable Weighted Average Remaining Weighted Weighted Contractual Average Average Number Term Exercise Number Exercise Range of Exercise Prices Outstanding (in years) Price Exercisable Price $ 43.71 — $ 43.71 1.4 2.21 $ 43.71 0.7 $ 43.71 46.17 — 46.87 0.9 0.97 46.33 0.9 46.33 49.55 — 56.86 1.3 3.21 56.83 0.3 56.81 70.74 — 70.74 1.1 4.21 70.74 — 70.74 79.59 — 79.59 1.2 5.20 79.59 — 79.59 86.17 — 86.17 1.6 6.20 86.17 — — $ 43.71 — $ 86.17 7.5 3.86 $ 65.09 1.9 $ 47.17

Deferred Compensation

Deferred Compensation	12 Months Ended
Deferred Compensation	Dec. 31, 2020
Compensation Related Costs [Abstract]
Deferred Compensation	11. Deferred Compensation We have a Deferred Equity Participation Plan, (which we refer to as the DEPP), which is a non-qualified plan that generally provides for distributions to certain of our key executives when they reach age 62 (or the one-year anniversary of the date of the grant for participants over the age of 61 as of the grant date) or upon or after their actual retirement if later. Under the provisions of the DEPP, we typically contribute cash in an amount approved by the compensation committee to a rabbi trust on behalf of the executives participating in the DEPP, and instruct the trustee to acquire a specified number of shares of our common stock on the open market or in privately negotiated transactions based on participant elections. Distributions under the DEPP may not normally be made until the participant reaches age 62 (or the one-year anniversary of the date of the grant for participants over the age of 61 as of the grant date) and are subject to forfeiture in the event of voluntary termination of employment prior to then. DEPP awards are generally made annually in the first quarter. In addition, we annually make awards under sub-plans of the DEPP for certain production staff, which generally provide for vesting and/or distributions no sooner than five years from the date of awards, although certain awards vest and/or distribute after the earlier of fifteen years or the participant reaching age 65. All contributions to the plan (including sub-plans) deemed to be invested in shares of our common stock are distributed in the form of our common stock and all other distributions are paid in cash. Our common stock that is issued to or purchased by the rabbi trust as a contribution under the DEPP is valued at historical cost, which equals its fair market value at the date of grant or date of purchase. When common stock is issued, we record an unearned deferred compensation obligation as a reduction of capital in excess of par value in the accompanying consolidated balance sheet, which is amortized to compensation expense ratably over the vesting period of the participants. Future changes in the fair market value of our common stock owed to the participants do not have any impact on the amounts recorded in our consolidated financial statements. In the first quarter of each of 2020, 2019 and 2018, the compensation committee approved $14.1 million, $10.1 million and $11.5 million, respectively, of awards in the aggregate to certain key executives under the DEPP that were contributed to the rabbi trust in the first quarters of 2020, 2019 and 2018. We contributed cash to the rabbi trust and instructed the trustee to acquire a specified number of shares of our common stock on the open market to fund these 2020, 2019 and 2018 awards. Dur In 2020, 2019 and 2018, the compensation committee approved $1.8 million, $2.6 million and $0.9 million, respectively, of awards under the sub‑plans referred to above, which were contributed to the rabbi trust in first quarter 2020, 2019 and 2018, respectively. During 2020, 2019 and 2018, we charged $1.9 million, $2.4 million and $2.2 million, respectively, to compensation expense related to these awards. There was $0.5 million of distributions from the sub-plans during 2019. There were no distributions from the sub-plans during 2020 and 2018. At December 31, 2020 and 2019, we recorded $60.5 million (related to 2.6 million shares) and $64.5 million (related to 2.9 million shares), respectively, of unearned deferred compensation as a reduction of capital in excess of par value in the accompanying consolidated balance sheet. The total intrinsic value of our unvested equity based awards under the plan at December 31, 2020 and 2019 was $327.8 million and $276.3 million, respectively. During 2020, 2019 and 2018, cash and equity awards with an aggregate fair value of $41.2 million, $3.1 million and $6.4 million, respectively, were vested and distributed to executives under the DEPP. We have a Deferred Cash Participation Plan (which we refer to as the DCPP), which is a non-qualified deferred compensation plan for certain key employees, other than executive officers, that generally provides for vesting and/or distributions no sooner than five years from the date of awards. Under the provisions of the DCPP, we typically contribute cash in an amount approved by the compensation committee to the rabbi trust on behalf of the executives participating in the DCPP, and instruct the trustee to acquire a specified number of shares of our common stock on the open market or in privately negotiated transactions based on participant elections. In the first quarter of each of 2020, 2019 and 2018, the compensation committee approved $3.0 million, $2.4 million and $5.6 million, respectively, of awards in the aggregate to certain key executives under the DCPP that were contributed to the rabbi trust in second quarter 2020, 2019 and 2018, respectively. In addition, the compensation committee approved $7.7 million and $1.6 million of awards in the aggregate to certain key executives under the DCPP that were contributed to the rabbi trust in the second and third quarters of 2019, respectively. During 2020, 2019 and 2018 we charged $6.9 million, $5.2 million and $3.0 million to compensation expense related to these awards. There was $3.2 million, $2.5 million and $3.6 million of distributions from the DCPP during 2020, 2019 and 2018, respectively.

Restricted Stock, Performance S

Restricted Stock, Performance Share and Cash Awards	12 Months Ended
Restricted Stock, Performance Share and Cash Awards	Dec. 31, 2020
Text Block [Abstract]
Restricted Stock, Performance Share and Cash Awards	12. Restricted Stock, Performance Share and Cash Awards Restricted Stock Awards As discussed in Note 10 to these consolidated financial statements, on May 16, 2017, our stockholders approved the LTIP, which replaced our previous stockholder-approved 2014 LTIP. The LTIP provides for the grant of a stock award either as restricted stock or as restricted stock units to officers, employees and non-employee directors. In either case, the compensation committee may determine that the award will be subject to the attainment of performance measures over an established performance period. Stock awards and the related dividend equivalents are non-transferable and subject to forfeiture if the holder does not remain continuously employed with us during the applicable restriction period or, in the case of a performance-based award, if applicable performance measures are not attained. The compensation committee will determine all of the terms relating to the satisfaction of performance measures and the termination of a restriction period, or the forfeiture and cancellation of a restricted stock award upon a termination of employment, whether by reason of disability, retirement, death or any other reason. The agreements awarding restricted stock units under the LTIP will specify whether such awards may be settled in shares of our common stock, cash or a combination of shares and cash and whether the holder will be entitled to receive dividend equivalents, on a current or deferred basis, with respect to such award. Prior to the settlement of a restricted stock unit, the holder of a restricted stock unit will have no rights as a stockholder of the company. The maximum number of shares available under the LTIP for restricted stock, restricted stock units and performance unit awards settled with stock (i.e., all awards other than stock options and stock appreciation rights) is 4.0 million. At December 31, 2020, 2.3 million shares were available for grant under the LTIP for such awards. In 2020, 2019 and 2018, we granted 422,610, 414,700 and 439,100 restricted stock units, respectively, to employees under the LTIP and 2014 LTIP, with an aggregate fair value of $34.9 million, $31.8 million and $28.7 million, respectively, at the date of grant. The 2020, 2019 and 2018 restricted stock units vest as follows: 405,870 units granted in first quarter 2020, 399,900 units granted in first quarter 2019 and 420,200 units granted in first quarter 2018 vest in full based on continued employment through March 12, 2025, March 14, 2024 and March 15, 2023, respectively, while the other 2020, 2019 and 2018 restricted stock unit awards generally vest in full based on continued employment through the vesting period on the anniversary date of the grant. For certain of our executive officers age 55 or older, restricted stock units awarded in 2020, 2019 and 2018 are not subject to forfeiture upon such officers’ departure from the company after two years from the date of grant. The vesting periods of the 2020, 2019 and 2018 restricted stock unit awards are as follows (in actual shares): Restricted Stock Units Granted Vesting Period 2020 2019 2018 One year 16,740 14,800 18,900 Two years 8,870 12,000 12,700 Five years 397,000 387,900 407,500 Total shares granted 422,610 414,700 439,100 We account for restricted stock awards at historical cost, which equals its fair market value at the date of grant, which is amortized to compensation expense ratably over the vesting period of the participants. Future changes in the fair value of our common stock that is owed to the participants do not have any impact on the amounts recorded in our consolidated financial statements. During 2020, 2019 and 2018, we charged $40.0 million, $29.8 million and $27.2 million, respectively, to compensation expense related to restricted stock awards granted in 2009 through 2020. The total intrinsic value of unvested restricted stock at December 31, 2020 and 2019 was $302.4 million and $215.1 million, respectively. During 2020 and 2019, equity awards (including accrued dividends) with an aggregate fair value of $2.0 million and $2.1 million were vested and distributed to employees under this plan. Performance Share Awards On March 12, 2020, March 14, 2019 and March 15, 2018, pursuant to the LTIP, the compensation committee approved 82,500, 73,600 and 78,200, respectively of provisional performance share awards, with an aggregate fair value of $7.1 million, $5.8 million and $5.3 million, respectively, for future grants to our officers and key employees. Each performance unit award was equivalent to the value of one share of our common stock on the date such provisional award was approved. At the end of the performance period, eligible participants will receive a number of earned shares based on the growth in adjusted EBITDAC per share (as defined in the 2020 Proxy Statement). Earned shares for the 2020, 2019 and 2018 provisional awards will fully vest based on continuous employment through March 12, 2023, March 14, 2022 and March 15, 2021, respectively, and will be settled in unrestricted shares of our common stock on a one-for-one basis as soon as practicable in 2023, 2022 and 2021, respectively. The 2020, 2019 and 2018 awards are subject to a three-year performance period that begins on January 1, 2020, 2019 and 2018, respectively, and vest on the three-year anniversary of the date of grant (March 12, 2023, March 14, 2022 and March 15, 2021). For certain of our executive officers age 55 or older, awards granted in 2020, 2019 and 2018 are no longer subject to forfeiture upon such officers’ departure from the company after two years from the date of grant. During 2020, 2019 and 2018, equity awards (including accrued dividends) with an aggregate fair value of $12.5 million, $5.7 million and $3.7 million was vested and distributed to employees under this plan. Cash Awards On March 12, 2020, pursuant to our Performance Unit Program (which we refer to as the Program), the compensation committee approved provisional cash awards of $18.4 million in the aggregate for future grants to our officers and key employees that are denominated in units (213,000 units in the aggregate), each of which was equivalent to the value of one share of our common stock on the date the provisional award was approved. The Program consists of a one-year three-year Based on company performance for 2020, we expect to grant 209,000 units under the Program in first quarter 2021 that will fully vest on January 1, 2023. On March 14, 2019, pursuant to the Program, the compensation committee approved provisional cash awards of $16.5 million in the aggregate for future grants to our officers and key employees that are denominated in units (206,800 units in the aggregate), each of which was equivalent to the value of one share of our common stock on the date the provisional award was approved. Terms of the 2019 provisional award were similar to the terms of the 2020 provisional awards. Based on our performance for 2019, we granted 200,000 units under the Program in first quarter 2020 that will fully vest on January 1, 2022. During 2020, we charged $10.6 million to compensation expense related to these awards. On March 15, 2018, pursuant to the Program, the compensation committee approved provisional cash awards of $15.0 million in the aggregate for future grants to our officers and key employees that are denominated in units (219,000 units in the aggregate), each of which was equivalent to the value of one share of our common stock on the date the provisional award was approved. Terms of the 2018 provisional award were similar to the terms of the 2019 provisional awards. Based on our performance for 2018, we granted 190,000 units under the Program in first quarter 2019 that fully vested on January 1, 2021. During 2020 and 2019, we charged $9.9 million and $8.9 million to compensation expense related to these awards. On March 16, 2017, pursuant to the Program, the compensation committee approved provisional cash awards of $14.3 million in the aggregate for future grants to our officers and key employees that are denominated in units (255,000 units in the aggregate), each of which was equivalent to the value of one share of our common stock on the date the provisional awards were approved. Terms of the 2017 provisional award were similar to the terms of the 2018 provisional awards. Based on our performance for 2017, we granted 242,000 units under the Program in first quarter 2018 that fully vested on January 1, 2020. During 2019 and 2018, we charged $10.3 million and $8.7 million to compensation expense related to these awards, respectively. On March 17, 2016, pursuant to the Program, the compensation committee approved provisional cash awards of $17.4 million in the aggregate for future grants to our officers and key employees that are denominated in units (397,000 units in the aggregate), each of which was equivalent to the value of one share of our common stock on the date the provisional award was approved. Terms of the 2016 provisional award were similar to the terms of the 2017 provisional awards. Based on our performance for 2016, we granted 385,000 units under the Program in first quarter 2017 that fully vested on January 1, 2019. During 2018, we charged $11.7 million to compensation expense related to these awards. During 2019, cash awards related to the 2016 provisional awards with an aggregate fair value of $22.4 million (341,000 units in the aggregate) were vested and distributed to employees under the Program. During 2018, cash awards related to the 2015 provisional awards with an aggregate fair value of $15.8 million (269,000 units in the aggregate) were vested and distributed to employees under the Program. During 2017, cash awards related to the 2014 provisional awards with an aggregate fair value of $9.3 million (199,000 units in the aggregate) were vested and distributed to employees under the Program.

Retirement Plans

Retirement Plans	12 Months Ended
Retirement Plans	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Retirement Plans	13. Retirement Plans We have a noncontributory defined benefit pension plan that, prior to July 1, 2005, covered substantially all of our domestic employees who had attained a specified age and one year of employment. Benefits under the plan were based on years of service and salary history. In 2005, we amended our defined benefit pension plan to freeze the accrual of future benefits for all U.S. employees, effective on July 1, 2005. Since the plan is frozen, there is no difference between the projected benefit obligation and accumulated benefit obligation at December 31, 2020 and 2019. In the table below, the service cost component represents plan administration costs that are incurred directly by the plan. A reconciliation of the beginning and ending balances of the pension benefit obligation and fair value of plan assets and the funded status of the plan is as follows (in millions): Year Ended December 31, 2020 2019 Change in pension benefit obligation: Benefit obligation at beginning of year $ 274.4 $ 253.2 Service cost 0.8 1.6 Interest cost 8.0 9.8 Net actuarial loss 22.6 24.7 Benefits paid (15.2 ) (14.9 ) Benefit obligation at end of year $ 290.6 $ 274.4 Change in plan assets: Fair value of plan assets at beginning of year $ 243.7 $ 220.0 Actual return on plan assets 34.3 38.6 Contributions by the company — — Benefits paid (15.2 ) (14.9 ) Fair value of plan assets at end of year $ 262.8 $ 243.7 Funded status of the plan (underfunded) $ (27.8 ) $ (30.7 ) Amounts recognized in the consolidated balance sheet consist of: Noncurrent liabilities - accrued benefit liability $ (27.8 ) $ (30.7 ) Accumulated other comprehensive loss - net actuarial loss 68.3 69.8 Net amount included in retained earnings $ 40.5 $ 39.1 The components of the net periodic pension benefit cost for the plan and other changes in plan assets and obligations recognized in earnings and other comprehensive earnings consist of the following (in millions): Year Ended December 31, 2020 2019 2018 Net periodic pension cost: Service cost $ 0.8 $ 1.6 $ 0.8 Interest cost on benefit obligation 8.0 9.8 9.3 Expected return on plan assets (16.4 ) (14.8 ) (16.0 ) Amortization of net loss 6.2 7.0 4.9 Net periodic benefit cost (1.4 ) 3.6 (1.0 ) Other changes in plan assets and obligations recognized in other comprehensive earnings: Net loss incurred 4.7 0.8 17.2 Amortization of net loss (6.2 ) (7.0 ) (4.9 ) Total recognized in other comprehensive loss (1.5 ) (6.2 ) 12.3 Total recognized in net periodic pension cost and other comprehensive loss $ (2.9 ) $ (2.6 ) $ 11.3 Estimated amortization for the following year: Amortization of net loss $ 5.8 $ 6.1 $ 7.2 The following weighted average assumptions were used at December 31 in determining the plan’s pension benefit obligation: December 31, 2020 2019 Discount rate 2.25 % 3.00 % Weighted average expected long-term rate of return on plan assets 7.00 % 7.00 % The following weighted average assumptions were used at January 1 in determining the plan’s net periodic pension benefit cost: Year Ended December 31, 2020 2019 2018 Discount rate 3.00 % 4.00 % 3.50 % Weighted average expected long-term rate of return on plan assets 7.00 % 7.00 % 7.00 % The following benefit payments are expected to be paid by the plan (in millions): 2021 $ 16.2 2022 16.5 2023 16.7 2024 16.7 2025 16.9 Years 2026 to 2030 83.1 The following is a summary of the plan’s weighted average asset allocations at December 31 by asset category: December 31, Asset Category 2020 2019 Equity securities 63.0 % 61.0 % Debt securities 30.0 % 32.0 % Real estate 7.0 % 7.0 % Total 100.0 % 100.0 % Plan assets are invested in various pooled separate accounts under annuity contracts managed by two life underwriting enterprises The weighted average expected long-term rate of return on plan assets assumption was determined based on a review of the asset allocation strategy of the plan using ten-year The following is a summary of the plan’s assets carried at fair value as of December 31 by level within the fair value hierarchy (in millions): December 31, Fair Value Hierarchy 2020 2019 Level 1 $ — $ — Level 2 141.8 135.8 Level 3 121.0 107.9 Total fair value $ 262.8 $ 243.7 The plan’s Level 2 assets consist of ownership interests in various pooled separate accounts within a life insurance carrier’s group annuity contract. The fair value of the pooled separate accounts is determined based on the net asset value of the respective funds, which is obtained from the underwriting enterprise underwriting enterprise insurance carrier’s annuity contracts for which fair value has been determined by an independent valuation. Due to the nature of these annuity contracts, our management makes assumptions to determine how a market participant would price these Level 3 assets. In determining fair value , the future cash flows to be generated by the annuity contracts were estimated using the underlying benefit provisions specified in each contract, market participant assumptions and various ac tuarial and financial models. T hese cash flows were then discounted to present value using a risk-adjusted rate that takes into consideration market based rates of return and probability-weighted present values. The following is a reconciliation of the beginning and ending balances for the Level 3 assets of the plan measured at fair value (in millions): Year Ended December 31, 2020 2019 Fair value at January 1 $ 107.9 $ 94.9 Settlements (2.7 ) — Unrealized gain 15.8 13.0 Fair value at December 31 $ 121.0 $ 107.9 We were not required under the IRC to make any minimum contributions to the plan for each of the 2020, 2019 and 2018 plan years. This level of required funding is based on the plan being frozen and the aggregate amount of our historical funding. During 2018 we made a $30.0 million discretionary contribution to the plan. During 2020 and 2019 we did not make discretionary contributions to the plan. We also have a qualified contributory savings and thrift 401(k) plan covering the majority of our domestic employees. For eligible employees who have met the plan’s age and service requirements to receive matching contributions, we historically have matched 100% of pre-tax and Roth elective deferrals up to a maximum of 5.0% of eligible compensation, subject to federal limits on plan contributions and not in excess of the maximum amount deductible for federal income tax purposes. Beginning in 2021, the amount matched by the company will be discretionary and annually determined by management. Employees must be employed and eligible for the plan on the last day of the plan year to receive a matching contribution, subject to certain exceptions enumerated in the plan document. Matching contributions are subject to a five-year We also have a nonqualified deferred compensation plan, the Supplemental Savings and Thrift Plan, for certain employees who, due to IRS rules, cannot take full advantage of our matching contributions under the 401(k) plan. The plan permits these employees to annually elect to defer a portion of their compensation until their retirement or a future date. Our matching contributions to this plan (up to a maximum of the lesser of a participant’s elective deferral of base salary, annual bonus and commissions or 5.0% of eligible compensation, less matching amounts contributed under the 401(k) plan) are also at the discretion of our board of directors. Matching contributions can be funded in cash or company stock. Our board of directors has authorized the use of common stock to fund our 2020 employer matching contributions to the plan, which we plan to do in February 2021. We expensed $7.8 million, $7.1 million and $6.5 million related to contributions made to a rabbi trust maintained under the plan in 2020, 2019 and 2018, respectively. The fair value of the assets in the plan’s rabbi trust at December 31, 2020 and 2019, including employee contributions and investment earnings, was $497.3 million and $452.9 million, respectively, and has been included in other noncurrent assets and the corresponding liability has been included in other noncurrent liabilities in the accompanying consolidated balance sheet. We also have several foreign benefit plans, the largest of which is a defined contribution plan that provides for us to make contributions of 5.0% of eligible compensation. In addition, the plan allows for voluntary contributions by U.K. employees, which we match 100%, up to a maximum of an additional 5.0% of eligible compensation. Net expense for foreign retirement plans amounted to $44.3 million, $39.8 million and $34.9 million in 2020, 2019 and 2018, respectively.

Investments

Investments	12 Months Ended
Investments	Dec. 31, 2020
Equity Method Investments And Joint Ventures [Abstract]
Investments	14. Investments The following is a summary of our investments included in other noncurrent assets in the consolidated balance sheet (in millions): December 31, 2020 2019 Assets Funding commitments Assets Chem-Mod LLC $ 4.0 $ - $ 4.0 Chem-Mod International LLC 2.0 - 2.0 Clean-coal investments: Controlling interest in limited liability companies that own fourteen 2009 Era Clean Coal Plants - - - Non-controlling interest in a limited liability company that owns one 2011 Era Clean Coal Plant 0.1 - 0.3 Controlling interest in limited liability companies that own twenty 2011 Era Clean Coal Plants 12.4 0.9 29.2 Other investments 3.9 4.5 Total investments $ 22.4 $ 0.9 $ 40.0 Chem-Mod LLC - At December 31, 2020, we held a 46.5% controlling interest in Chem-Mod LLC. Chem‑Mod LLC possesses the exclusive marketing rights, in the U.S. and Canada, for technologies used to reduce emissions created during the combustion of coal. The refined coal production plants discussed below, as well as those owned by other unrelated parties, license and use Chem-Mod LLC’s proprietary technologies, The Chem-Mod™ Solution, in the production of refined coal. The Chem‑Mod™ Solution uses a dual injection sorbent system to reduce mercury, sulfur dioxide and other emissions at coal-fired power plants. We believe that the application of The Chem-Mod™ Solution qualifies for refined coal tax credits under IRC Section 45 when used with refined coal production plants placed in service by December 31, of both 2011 and 2009. Chem-Mod LLC has been marketing its technologies principally to coal-fired power plants owned by utility companies, including those utilities that are operating with the IRC Section 45 refined coal production plants in which we hold an investment. Chem-Mod LLC is determined to be a variable interest entity (which we refer to as a VIE). We are the manager (decision maker) of Chem‑Mod LLC and therefore consolidate its operations into our consolidated financial statements. At December 31, 2020, total assets and total liabilities of this VIE included in our consolidated balance sheet were $19.0 million and $4.4 million, respectively. At December 31, 2019, total assets and total liabilities of this VIE included in our consolidated balance sheet were $16.3 million and $2.8 million, respectively. For 2020, total revenues and expenses were $74.3 million and $10.6 million, respectively. For 2019, total revenues and expenses were $81.9 million and $17.5 million, respectively. We are under no obligation to fund Chem-Mod’s operations in the future. Chem-Mod International LLC - At December 31, 2020, we held a 31.5% noncontrolling ownership interest in Chem-Mod International LLC. Chem-Mod International LLC has the rights to market The Chem-Mod™ Solution in countries other than the U.S. and Canada. Such marketing activity has been limited to date. C-Quest Technology LLC and C-Quest Technologies International LLC (which we refer together as C-Quest) - At December 31, 2020, we held a noncontrolling 12% interest in C-Quest’s global entities. C‑Quest possesses rights, information and technology for the reduction of carbon dioxide emissions created by burning fossil fuels. Thus far, C‑Quest’s operations have been limited to laboratory testing. C-Quest is determined to be a VIE, but we do not consolidate this investment into our consolidated financial statements because we are not the primary beneficiary or decision maker. Clean Coal Investments - • We have investments in limited liability companies that own 35 refined coal production plants which produce refined coal using proprietary technologies owned by Chem-Mod LLC. We believe the production and sale of refined coal at these plants is qualified to receive refined coal tax credits under IRC Section 45. The 14 plants placed in service prior to December 31, 2009 (which we refer to as the 2009 Era Plants) were eligible to receive tax credits through 2019 and the 21 plants placed in service prior to December 31, 2011 (which we refer to as the 2011 Era Plants) are eligible to receive tax credits through 2021. • As of December 31, 2020: o Twenty o We have a noncontrolling interest in one plant, which is owned by a limited liability company (which we refer to as a LLC). We have determined that this LLC is a VIE, for which we are not the primary beneficiary and therefore do not consolidate it. At December 31, 2020, total assets and total liabilities of this VIE were $36.6 million and $36.0 million, respectively. For 2020, total revenues and expenses of this VIE were $35.2 million and $43.9 million, respectively. • We and our co-investors each fund our portion of the on-going operations of the limited liability companies in proportion to our investment ownership percentages. Other than our portion of the on-going operational funding, there are no additional amounts that we are committed to related to funding these investments. Other Investments - At December 31, 2020, we owned a non-controlling, minority interest in four venture capital funds totaling $3.9 million and eight certified low-income housing developments with zero carrying value. The low-income housing developments and real estate entities have been determined to be VIEs, but are not required to be consolidated due to our lack of control over their respective operations. At December 31, 2020, total assets and total liabilities of these VIEs were approximately $4.8 million and $0.5 million, respectively

Leases

Leases	12 Months Ended
Leases	Dec. 31, 2020
Leases [Abstract]
Leases	15. Leases We have operating leases primarily related to branch facilities, data centers, sales offices, and agent locations, automobiles and office equipment. Many of our leases include both lease (fixed rent payments) and non-lease components (common-area or other maintenance costs) which are accounted for as a single lease component as we have elected the practical expedient to group lease and non-lease components for all leases. Variable lease payments, such as periodically indexed and/or market adjustments, are presented as lease expense in the period in which they are incurred. Since we did not elect the short-term policy election, we record leases of 12 months or less on the balance sheet. We exclude options to extend or terminate a lease from our recognition as part of our right-of-use assets and lease liabilities until those options are reasonably certain and/or executed. We do not have any material guarantees, options to purchase, or restrictive covenants related to our leases. As our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at the lease commencement date in determining the present value of the lease payments. We consider qualitative factors including our derived credit rating, notched adjustments for collateralization, lease term, and, if significant, adjustments to our collateralized rate to borrow in the same currency in which the lease is denominated. The components of lease expense are as follows (in millions): Statement of Earnings Year ended Lease Components Classification December 31, 2020 Operating lease expense Operating expense $ 126.5 Variable lease expense Operating expense 22.0 Sublease income Investment income (1.1 ) Total net lease expense $ 147.4 Variable lease cost consist primarily of common-area and other maintenance costs for our lease facilities, as well as variable lease payments related to indexed and/or market adjustments. Our sublease income derives primarily from a few office lease arrangements and we have no significant sublease losses. Year ended Supplemental Cash Flow Information Related to Leases (in millions) December 31, 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 120.1 Right-of-use assets obtained in exchange for new operating lease liabilities $ 71.2 We present all noncash transactions related to adjustments to the lease liability or right-of-use asset as noncash transactions. This includes all noncash charges related to any modification or reassessment events triggering remeasurement. Supplemental balance sheet information related to leases is as follows (in millions, except lease term and discount rate): Lease Components Balance Sheet Classification December 31, 2020 Lease right-of-use assets Right-of-use assets $ 373.9 Other current lease liabilities Accrued compensation and other current liabilities 88.8 Lease liabilities Lease liabilities - noncurrent 320.9 Total lease liabilities $ 409.7 Weighted-average remaining lease term, years 5.3 Weighted-average discount rate 3.6 % Maturities of operating lease liabilities for each of the next five years and thereafter are as follows (in millions): 2021 $ 108.5 2022 93.9 2023 75.1 2024 54.8 2025 41.6 Thereafter 77.8 Total lease payments 451.7 Less interest (42.0 ) Total $ 409.7 Our leases have remaining lease terms of 0.1 years to 11.7 years, some of which may include options to extend the leases for up to 5.0 years and some of which may include options to terminate the leases. As of December 31, 2020, we have additional leases that have not yet commenced of $0.3 million. These leases will commence in 2021 with lease terms of 0.5 years to 5.4 years.

Derivatives and Hedging Activit

Derivatives and Hedging Activity	12 Months Ended
Derivatives and Hedging Activity	Dec. 31, 2020
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivatives and Hedging Activity	16. Derivatives and Hedging Activity We adopted ASU 2017-12 on January 1, 2019. Among other provisions, the new standard required modification to existing presentation and disclosure requirements on a prospective basis. As such, certain disclosures below conform to the disclosure requirements prior to the adoption of ASU 2017-12. We are exposed to market risks, including changes in foreign currency exchange rates and interest rates. To manage the risk related to these exposures, we enter into various derivative instruments that reduce these risks by creating offsetting exposures. We generally do not enter into derivative transactions for trading or speculative purposes. Foreign Exchange Risk Management We are exposed to foreign exchange risk when we earn revenues, pay expenses, or enter into monetary intercompany transfers denominated in a currency that differs from our functional currency, or other transactions that are denominated in a currency other than our functional currency. We use foreign exchange derivatives, typically forward contracts and options, to reduce our overall exposure to the effects of currency fluctuations on cash flows. These exposures are hedged, on average, for less than three years. Interest Rate Risk Management We enter into various long-term debt agreements. We use interest rate derivatives, typically swaps, to reduce our exposure to the effects of interest rate fluctuations on the forecasted interest rates for up to three years into the future. We have not received or pledged any collateral related to derivative arrangements at December 31, 2020. The notional and fair values of derivatives designated as hedging instruments are as follows at December 31, 2020 and 2019 (in millions): Derivative Assets Derivative Liabilities Notional Balance Sheet Fair Balance Sheet Fair Instrument Amount Classification Value Classification Value At December 31, 2020 Interest rate contracts $ 550.0 Other current assets $ — Accrued compensation and $ 54.5 Other noncurrent assets — other current liabilities Other noncurrent liabilities 10.9 Foreign exchange contracts (1) 48.6 Other current assets 5.9 Accrued compensation and 0.6 other current liabilities Other noncurrent assets 7.8 Other noncurrent liabilities 3.3 Total $ 598.6 $ 13.7 $ 69.3 At December 31, 2019 Interest rate contracts $ 800.0 Other current assets $ 2.8 Accrued compensation and $ 25.0 Other noncurrent assets 5.4 other current liabilities Other noncurrent liabilities 23.0 Foreign exchange contracts (1) 31.7 Other current assets 4.5 Accrued compensation and 1.8 other current liabilities Other noncurrent assets 8.5 Other noncurrent liabilities 2.6 Total $ 831.7 $ 21.2 $ 52.4 ( 1) Included within foreign exchange contracts at December 31, 2020 were $354.7 million of call options offset with $354.7 million of put options, and $9.0 million of buy forwards offset with $57.6 million of sell forwards. Fair values of these hedge contracts are based on observable and unobservable inputs. Observable inputs include all of the following: quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (for example: interest rates and yield curves observable at commonly quoted intervals, implied volatilities, credit spreads) and market-corroborated inputs. Unobservable inputs are used to measure fair value to the extent that relevant observable inputs are not available, thereby allowing for situations in which there is little, if any, market activity for the asset or liability at the measurement date. The effect of cash flow hedge accounting on accumulated other comprehensive loss were as follows (in millions): Instrument Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss (1) Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Earnings Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing Statement of Earnings Classification Year ended December 31, 2020 Interest rate contracts $ (92.5 ) $ (1.1 ) $ — Interest expense Foreign exchange contracts (4.6 ) (2.4 ) (0.4 ) Commission revenue (1.6 ) 1.6 Compensation expense (1.2 ) 1.1 Operating expense Total $ (97.1 ) $ (6.3 ) $ 2.3 Year ended December 31, 2019 Interest rate contracts $ (47.0 ) $ (1.2 ) $ — Interest expense Foreign exchange contracts 9.9 (1.6 ) (0.8 ) Commission revenue (1.4 ) 1.2 Compensation expense (1.0 ) 0.9 Operating expense Total $ (37.1 ) $ (5.2 ) $ 1.3 (1) During 2020, the amount excluded from the assessment of hedge effectiveness for our foreign exchange contracts recognized in accumulated other comprehensive loss was a loss of $1.3 million. We estimate that approximately $2.5 million of pretax loss currently included within accumulated other comprehensive loss will be reclassified into earnings in the next twelve months.

Commitments, Contingencies and

Commitments, Contingencies and Off-Balance Sheet Arrangements	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments, Contingencies and Off-Balance Sheet Arrangements	17. In connection with our investing and operating activities, we have entered into certain contractual obligations and commitments. See Notes 8 and 14 to these consolidated financial statements for additional discussion of these obligations and commitments. Our future minimum cash payments, including interest, associated with our contractual obligations pursuant to the note purchase agreements, Credit Agreement, Premium Financing Debt Facility, operating leases and purchase commitments at December 31, 2020 were as follows (in millions): Payments Due by Period Contractual Obligations 2021 2022 2023 2024 2025 Thereafter Total Note purchase agreements $ 75.0 $ 200.0 $ 250.0 $ 475.0 $ 200.0 $ 3,148.0 $ 4,348.0 Credit Agreement — — — — — — — Premium Financing Debt Facility 203.6 — — — — — 203.6 Interest on debt 189.5 183.6 174.7 158.0 143.4 601.9 1,451.1 Total debt obligations 468.1 383.6 424.7 633.0 343.4 3,749.9 6,002.7 Operating lease obligations 108.5 93.9 75.1 54.8 41.6 77.8 451.7 Less sublease arrangements (0.3 ) (0.3 ) (0.2 ) (0.2 ) (0.2 ) (0.5 ) (1.7 ) Outstanding purchase obligations 75.3 49.4 30.8 21.9 16.7 22.7 216.8 Total contractual obligations $ 651.6 $ 526.6 $ 530.4 $ 709.5 $ 401.5 $ 3,849.9 $ 6,669.5 The amounts presented in the table above may not necessarily reflect our actual future cash funding requirements, because the actual timing of the future payments made may vary from the stated contractual obligation. As of December 31, 2020, we had a $48.2 million accrued liability related to the Ashton Tiffany acquisition that is not in the foregoing table that may be settled using shares of our common stock in early February 2021. On December 23, 2020, we signed a definitive agreement to acquire 100% of the equity of The Bollington Wilson Group (which we refer to as Bollington) headquartered in Sale, Greater Manchester, U.K., for approximately $330.0 million of cash consideration. The transaction is subject to regulatory approval, which was received on January 26, 2021, and is expected to close in February 2021. Note Purchase Agreements, Credit Agreement and Premium Financing Debt Facility - See Note 8 to these consolidated financial statements for a summary the amounts outstanding under the note purchase agreements, the Credit Agreement and Premium Debt Facility. Operating Lease Obligations - Our corporate segment’s executive offices and certain subsidiary and branch facilities of our brokerage and risk management segments are located in a building we own at 2850 Golf Road, Rolling Meadows, Illinois, where we have approximately 360,000 square feet of space and will accommodate approximately 2,000 employees at peak pre-pandemic capacity. During first quarter 2017, we relocated our corporate office headquarters to the Rolling Meadows location. Relating to the development of our corporate headquarters, we expect to receive property tax related credits under a tax-increment financing note from Rolling Meadows and an Illinois state Economic Development for a Growing Economy (which we refer to as EDGE) tax credit. Incentives from these two programs could total between $60.0 million and $90.0 million over a fifteen-year We generally operate in leased premises at our other locations. Certain of these leases have options permitting renewals for additional periods. In addition to minimum fixed rentals, a number of leases contain annual escalation clauses which are generally related to increases in an inflation index. Total rent expense, including rent relating to cancelable leases and leases with initial terms of less than one year, amounted to $154.0 million in 2020, $148.1 million in 2019 and $140.0 million in 2018. We have leased certain office space to several non-affiliated tenants under operating sublease arrangements. In the normal course of business, we expect that certain of these leases will not be renewed or replaced. We adjust charges for real estate taxes and common area maintenance annually based on actual expenses, and we recognize the related revenues in the year in which the expenses are incurred. These amounts are not included in the minimum future rentals to be received in the contractual obligations table above. Outstanding Purchase Obligations - We typically do not have a material amount of outstanding purchase obligations at any point in time. The amount disclosed in the contractual obligations table above represents the aggregate amount of unrecorded purchase obligations that we had outstanding at December 31, 2020. These obligations represent agreements to purchase goods or services that were executed in the normal course of business. Off-Balance Sheet Commitments Our total unrecorded commitments associated with outstanding letters of credit, financial guarantees and funding commitments at December 31, 2020 were as follows (in millions): Amount of Commitment Expiration by Period Off-Balance Sheet Commitments 2021 2022 2023 2024 2025 Thereafter Total Amounts Committed Letters of credit $ — $ — $ — $ — $ — $ 18.4 $ 18.4 Financial guarantees 0.2 0.2 0.2 0.2 0.2 0.2 1.2 Total commitments $ 0.2 $ 0.2 $ 0.2 $ 0.2 $ 0.2 $ 18.6 $ 19.6 Since commitments may expire unused, the amounts presented in the table above do not necessarily reflect our actual future cash funding requirements. See Note 14 to these consolidated financial statements for a discussion of our funding commitments related to our corporate segment and the Off-Balance Sheet Debt section below for a discussion of other . All of the represent multiple year commitments that have annual, automatic renewing provisions and are classified by the latest commitment date. Since January 1, 2002, we have acquired 583 companies, all of which were accounted for using the acquisition method for recording business combinations. Substantially all of the purchase agreements related to these acquisitions contain provisions for potential earnout obligations. For all of our acquisitions made in the period from 2016 to 2020 that contain potential earnout obligations, such obligations are measured at fair value as of the acquisition date and are included on that basis in the recorded purchase price consideration for the respective acquisition. The amounts recorded as earnout payables are primarily based upon estimated future potential operating results of the acquired entities over a two- to three-year period subsequent to the acquisition date. The aggregate amount of the maximum earnout obligations related to these acquisitions was $1,128.1 million, of which $592.2 million was recorded in our consolidated balance sheet as of December 31, 2020 based on the estimated fair value of the expected future payments to be made, of which approximately $493.7 million can be settled in cash or stock at our option and $98.5 million must be settled in cash. Off-Balance Sheet Debt - Our unconsolidated investment portfolio includes investments in enterprises where our ownership interest is between 1 % and 50 %, in which management has determined that our level of influence and economic interest is not sufficient to require consolidation . As a result, these investments are accounted for under the equity method. None of these unconsolidated investments had any outstanding debt at Decembe r 31 , 2020 and 2019 that was recourse to us. At December 31, 2020, we had posted two letters of credit totaling $9.4 million in the aggregate, related to our self-insurance deductibles, for which we had a recorded liability of $17.5 million. We have an equity investment in a rent-a-captive facility, which we use as a placement facility for certain of our insurance brokerage operations. At December 31, 2020, we had posted seven letters of credit totaling $7.5 million to allow certain of our captive operations to meet minimum statutory surplus requirements plus additional collateral related to premium and claim funds held in a fiduciary capacity, one letter of credit totaling $1.0 million for collateral related to claim funds held in a fiduciary capacity by a recent acquisition, and one letter of credit totaling $0.5 million as a security deposit for a 2015 acquisition’s lease. These letters of credit have never been drawn upon. Our commitments associated with outstanding letters of credit, financial guarantees and funding commitments at December 31, 2020 were as follows (all dollar amounts in table are in millions): Description, Purpose and Trigger Collateral Compensation to Us Maximum Exposure Liability Recorded Credit support under letters of credit (LOC) for deductibles due by us on our own insurance coverages - expires after 2025 None None $ 9.4 $ 17.5 Trigger - We do not reimburse the insurance companies for deductibles the insurance companies advance on our behalf Credit enhancement under letters of credit for our captive insurance operations to meet minimum statutory capital requirements - expires after 2025 None Reimbursement of LOC fees 7.5 - Trigger - Dissolution or catastrophic financial results of the operation Collateral related to claims funds held in a fiduciary capacity by a recent acquisition - expires 2021 None None 1.0 - Trigger - Claim payments are not made Credit support under letters of credit in lieu of a security deposit for an acquisition's lease - expires after 2025 None None 0.5 - Trigger - Lease payments do not get made Financial guarantees of loans to 5 Canadian-based employees - expires when loan balances are reduced to zero through May 2029 - Principal and interest payments are paid quarterly (1) None 1.2 - Trigger - Default on loan payments $ 19.6 $ 17.5 (1) The guarantees are collateralized by shares in minority holdings of our Canadian operating companies. Since commitments may expire unused, the amounts presented in the table above do not necessarily reflect our actual future cash funding requirements. Litigation, Regulatory and Taxation Matters - We are a defendant in various legal actions incidental to the nature of our business including but not limited to matters related to employment practices, alleged breaches of non-compete or other restrictive covenants, theft of trade secrets, breaches of fiduciary duties and related causes of action. We are also periodically the subject of inquiries, investigations and reviews by regulatory and taxing authorities into various matters related to our business, including our operational, compliance and finance functions. Neither the outcomes of these matters nor their effect upon our business, financial condition or results of operations can be determined at this time. On July 17, 2019, Midwest Energy Emissions Corp. and MES Inc. (which we refer to together as Midwest Energy) filed a patent infringement lawsuit in the United States District Court for the District of Delaware against us, Chem ‑Mod LLC and numerous other related and unrelated parties. The complaint alleges that the named defendants infringe patents held exclusively by Midwest Energy and seeks unspecified damages and injunctive relief. On July 15, 2020, the district court dismissed Midwest Energy’s complaint without prejudice. On the same day, Midwest Energy filed an amended complaint. We filed a motion to dismiss the amended complaint, and Midwest Energy subsequently filed a second amended complaint , which we again have moved to dismiss . We continue to defend this matter vigorously. Litigation is inherently uncertain and it is not possible for us to predict the ultimate outcome of this matter and the financial impact to us. We believe the probability of a material loss is remote. As previously disclosed, our IRC 831(b) (or “micro-captive”) advisory services businesses has been under investigation by the IRS since 2013. Among other matters, the IRS is investigating whether we have been acting as a tax shelter promotor in connection with these operations. Additionally, the IRS has initiated audits for the 2012 tax year, and subsequent tax years, of over 100 of the micro-captive underwriting enterprises In May 2020 we learned that the DOJ is conducting a criminal investigation related to IRC 831(b) micro-captive underwriting enterprises. We have been advised that we are not currently a target of the investigation. In June 2020 our subsidiary Artex Risk Solutions, Inc. (which we refer to as Artex) received a grand jury subpoena requesting documents relating to its micro-captive advisory business. We have produced documents in response to the subpoena. We are fully cooperating with both the IRS investigation and the DOJ investigation. We are not able to reasonably estimate the amount of any potential loss in connection with these investigations. On December 7, 2018, a class action lawsuit was filed against us, Artex and other defendants in the United States District Court for the District of Arizona. The named plaintiffs are micro-captives and related entities and owners who had IRS Section 831(b) tax benefits disallowed by the IRS. The complaint alleges that the defendants defrauded the plaintiffs by marketing and managing micro‑captives with the knowledge that the captives did not constitute bona fide insurance and thus would not qualify for tax benefits. The complaint does not specify the amount of damages sought by the named plaintiffs. On August 5, 2019, the trial court granted the defendants’ motion to compel arbitration and dismissed the class action lawsuit. Plaintiffs appealed this ruling to the United States Court of Appeals for the Ninth Circuit. On September 9, 2020, the Ninth Circuit Court affirmed the ruling of the trial court dismissing the class action lawsuit. We will continue to defend against the lawsuit vigorously. Litigation is inherently uncertain, however, and it is not possible for us to predict the ultimate outcome of this matter and the financial impact to us, nor are we able to reasonably estimate the amount of any potential loss in connection with this lawsuit. Contingent Liabilities - We purchase insurance to provide protection from errors and omissions (which we refer to as E&O) claims that may arise during the ordinary course of business. Currently we retain the first $10.0 million of every E&O claim up to $10.0 million. In addition, we retain, in aggregate: up to another $4.5 million between $10.0 million and $100.0 million, plus up to another $20.0 million between $100.0 million and $240.0 million, and up to another $27.0 million between $240.0 million and 350.0 million. We have historically maintained self-insurance reserves for the portion of our E&O exposure that is not insured. We periodically determine a range of possible reserve levels using actuarial techniques that rely heavily on projecting historical claim data into the future. Our E&O reserve in the December 31, 2020 consolidated balance sheet is above the lower end of the most recently determined actuarial range by $2.6 million and below the upper end of the actuarial range by $6.4 million. In addition to this E&O reserve, in 2020, we established provisions for potential unusual pandemic related claim defense and other costs. We can make no assurances that the historical claim data used to project the current reserve levels will be indicative of future claim activity. Thus, the E&O reserve level and corresponding actuarial range could change in the future as more information becomes known, which could materially impact the amounts reported and disclosed herein. Tax-advantaged Investments No Longer Held - Between 1996 and 2007, we developed and then sold portions of our ownership in various energy related investments, many of which qualified for tax credits under IRC Section 29. We recorded tax benefits in connection with our ownership in these investments. At December 31, 2020, we had exposure on $108.0 million of previously earned tax credits . Under the TCJA, a portion of these previously earned tax credits were refunded in 2019 for tax year 2018, according to a specific formula. Under the Coronavirus Act, Relief, and Economic Security Act (the CARES Act), which was passed on March 27, 2020, we accelerated the refund of all remaining credits on April 17, 2020, and the remaining credits were refunded to us in the second quarter of 2020. In 2004, 2007 and 2009, the IRS examined several of these investments and all examinations were closed without any changes being proposed by the IRS. However, any future adverse tax audits, administrative rulings or judicial decisions could disallow previously claimed tax credits. Due to the contingent nature of this exposure and our related assessment of its likelihood, no reserve has been recorded in our December 31, 2020 consolidated balance sheet related to this exposure.

Insurance Operations

Insurance Operations	12 Months Ended
Insurance Operations	Dec. 31, 2020
Insurance [Abstract]
Insurance Operations	18. Insurance Operations We have ownership interests in several underwriting enterprises We have a wholly owned underwriting enterprise Reconciliations of direct to net premiums, on a written and earned basis, for 2020, 2019 and 2018 related to the wholly-owned underwriting enterprise subsidiary 2020 2019 2018 Written Earned Written Earned Written Earned Direct $ 37.7 $ 40.7 $ 44.6 $ 59.1 $ 57.6 $ 53.2 Assumed 0.1 0.9 1.0 1.9 4.7 4.6 Ceded (37.8 ) (41.6 ) (45.6 ) (61.0 ) (62.3 ) (57.8 ) Net $ - $ - $ - $ - $ - $ - At December 31, 2020 and 2019, our underwriting enterprise subsidiary our reinsurers or captives and have been .

Income Taxes

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	19. Income Taxes We and our principal domestic subsidiaries are included in a consolidated U.S. federal income tax return. Our international subsidiaries file various income tax returns in their jurisdictions. Earnings before income taxes in the table below include the impact of intercompany interest expense between domestic and foreign legal entities. Domestic intercompany interest income and offsetting foreign intercompany interest expense were $24.0 million in 2020, $40.1 million in 2019 and $65.8 million in 2018. Significant components of earnings before income taxes and the provision for income taxes are as follows (in millions): Year Ended December 31, 2020 2019 2018 Earnings before income taxes: United States $ 524.4 $ 388.4 $ 337.6 Foreign, principally Australia, Canada, New Zealand and the U.K. 346.5 237.7 141.8 Total earnings before income taxes $ 870.9 $ 626.1 $ 479.4 Provision (benefit) for income taxes: Federal: Current $ 43.6 $ 3.8 $ — Deferred (112.4 ) (142.5 ) (214.0 ) (68.8 ) (138.7 ) (214.0 ) State and local: Current 36.6 11.1 15.4 Deferred (19.3 ) (6.0 ) (29.0 ) 17.3 5.1 (13.6 ) Foreign: Current 94.6 66.6 60.7 Deferred (30.3 ) (22.7 ) (29.6 ) 64.3 43.9 31.1 Total provision (benefit) for income taxes $ 12.8 $ (89.7 ) $ (196.5 ) A reconciliation of the provision for income taxes with the U.S. federal statutory income tax rate is as follows (in millions, except percentages): Year Ended December 31, 2020 2019 2018 Amount % of Pretax Earnings Amount % of Pretax Earnings Amount % of Pretax Earnings Federal statutory rate $ 182.9 21.0 $ 131.5 21.0 $ 100.7 21.0 State income taxes - net of Federal benefit 22.2 2.6 4.4 0.7 8.5 1.8 Differences related to non U.S. operations (2.5 ) (0.3 ) (10.1 ) (1.6 ) (14.8 ) (3.1 ) Alternative energy and other tax credits (154.3 ) (17.7 ) (196.1 ) (31.3 ) (252.9 ) (52.8 ) Other permanent differences (15.7 ) (1.8 ) (7.6 ) (1.2 ) 0.9 0.2 U.S. repatriation tax - - - - (1.8 ) (0.4 ) Stock-based compensation (31.4 ) (3.6 ) (16.2 ) (2.6 ) (15.0 ) (3.1 ) Changes in unrecognized tax benefits - - 0.8 0.1 (0.2 ) - Change in valuation allowance 6.5 0.7 7.5 1.2 (22.0 ) (4.6 ) Change in tax rates 5.5 0.6 (3.7 ) (0.6 ) - - Other (0.4 ) - (0.2 ) - 0.1 - Provision (benefit) for income taxes $ 12.8 $ 1.5 $ (89.7 ) $ (14.3 ) $ (196.5 ) $ (41.0 ) A reconciliation of the beginning and ending balances of the total amounts of gross unrecognized tax benefits is as follows (in millions): December 31, 2020 2019 Gross unrecognized tax benefits at January 1 $ 11.5 $ 10.7 Increases in tax positions for current year 2.9 2.1 Settlements (1.1 ) (0.4 ) Lapse in statute of limitations (1.2 ) (1.1 ) Increases in tax positions for prior years 0.2 0.6 Decreases in tax positions for prior years (1.1 ) (0.4 ) Gross unrecognized tax benefits at December 31 $ 11.2 $ 11.5 The total amount of net unrecognized tax benefits that, if recognized, would affect the effective tax rate was $9.5 million and $9.4 million at December 31, 2020 and 2019, respectively. We accrue interest and penalties related to unrecognized tax benefits in our provision for income taxes. At December 31, 2020 and 2019, we had accrued interest and penalties related to unrecognized tax benefits of $3.0 million and $3.1 million, respectively. We file income tax returns in the U.S. and in various state, local and foreign jurisdictions. We are routinely examined by tax authorities in these jurisdictions. At December 31, 2020, our corporate returns had been examined by the IRS through calendar year 2010. The IRS is currently conducting various examinations of calendar years 2011 and 2012. In addition, a number of foreign, state, local and partnership examinations for later years are currently ongoing. It is reasonably possible that our gross unrecognized tax benefits may change within the next twelve months. However, we believe any changes in the recorded balance would not have a significant impact on our consolidated financial statements. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of our deferred tax assets and liabilities are as follows (in millions): December 31, 2020 2019 Deferred tax assets: Alternative minimum tax and other credit carryforwards $ 998.0 $ 962.1 Accrued and unfunded compensation and employee benefits 239.9 156.0 Amortizable intangible assets 61.3 54.3 Compensation expense related to stock options 14.4 11.3 Accrued liabilities 65.7 63.9 Accrued pension liability 9.3 9.9 Investments 1.3 0.9 Net operating loss carryforwards 36.1 37.2 Capital loss carryforwards 9.0 12.6 Lease liabilities 96.3 65.3 Hedging instruments 34.6 11.7 Other 2.8 4.3 Total deferred tax assets 1,568.7 1,389.5 Valuation allowance for deferred tax assets (94.9 ) (80.5 ) Deferred tax assets 1,473.8 1,309.0 Deferred tax liabilities: Nondeductible amortizable intangible assets 316.9 322.4 Investment-related partnerships 8.5 9.1 Depreciable fixed assets 32.4 22.4 Right-of-use assets 92.2 62.6 Revenue recognition 33.1 63.7 Other prepaid items 12.0 10.6 Total deferred tax liabilities 495.1 490.8 Net deferred tax assets $ 978.7 $ 818.2 At December 31, 2020 and 2019, $106.9 million and $127.5 million, respectively, have been included in noncurrent liabilities in the accompanying consolidated balance sheet. AMT credits have been utilized or refunded in 2020, due to the CARES Act legislation, general business and other tax credits of $983.0 million begin to expire, if not utilized, in 2034 and state credits, net of federal benefit, of $15.0 million expire, if not used, by 2025. Net operating loss carryforwards of $36.1 million, related to federal, state and foreign begin to expire, if not utilized in 2023. We expect the historically favorable trend in earnings before income taxes to continue in the foreseeable future. Accordingly, we expect to make full use of the net deferred tax assets. Valuation allowances have been established for certain foreign intangible assets and various net operating loss carryforwards that may not be utilized in the future. At December 31, 2020, foreign earnings in all jurisdictions are considered indefinitely reinvested offshore. Current U.S. tax law requires U.S. shareholders to include in income certain “global intangible low-taxed income” (which we refer to as GILTI) beginning in 2018. Our policy is to include the GILTI income in the future period when the tax arises and we recorded income tax expense on such income in 2020, 2019 and 2018. Current U.S. tax law includes the U.S. Base Erosion and Anti-Abuse Tax (which we refer to as BEAT) beginning in 2018. Based on our analysis, we determined that our base erosion payments do not exceed the threshold for applicability for the years in 2020, 2019 and 2018, and we do not currently anticipate any significant long-term impact from the BEAT in our provision for income taxes in future periods. On March 27, 2020, the CARES Act was enacted in response to the COVID-19 pandemic. The CARES Act contains several significant business tax provisions that could affect a company’s accounting for income taxes. See discussion of the various impacts of the CARES Act below. Deferred Income Taxes - In the 2018 consolidated financial statements, we finalized the revaluation of our net deferred tax asset as a result of the TCJA by recognizing an additional $2.9 million net benefit to the provision for income taxes.

Supplemental Disclosures of Cas

Supplemental Disclosures of Cash Flow Information	12 Months Ended
Supplemental Disclosures of Cash Flow Information	Dec. 31, 2020
Cash And Cash Equivalents [Abstract]
Supplemental Disclosures of Cash Flow Information	20. Supplemental Disclosures of Cash Flow Information Year ended December 31, Supplemental disclosures of cash flow information (in millions): 2020 2019 2018 Interest paid $ 188.9 $ 169.2 $ 139.2 Income taxes paid, net 113.0 22.2 68.1 Income taxes paid in the table above were net of AMT credit and other U.S. federal refunds of ($28.5) million in 2020, ($63.6) million in 2019 and ($2.4) million in 2018. The following is a reconciliation of our end of period cash, cash equivalents and restricted cash balances as presented in the consolidated statement of cash flows for the years ended December 31, 2020, 2019 and 2018 (in millions): December 31, 2020 2019 2018 Cash and cash equivalents $ 664.6 $ 604.8 $ 607.2 Restricted cash 2,909.7 2,019.1 1,629.6 Total cash, cash equivalents and restricted cash $ 3,574.3 $ 2,623.9 $ 2,236.8 We have a qualified contributory savings and thrift 401(k) plan covering the majority of our domestic employees. For eligible employees who have met the plan’s age and service requirements to receive matching contributions, we historically have matched 100% of pre-tax and Roth elective deferrals up to a maximum of 5.0% of eligible compensation, subject to federal limits on plan contributions and not in excess of the maximum amount deductible for federal income tax purposes. Beginning in 2021, the amount matched by the company will be discretionary and annually determined by management. Employees must be employed and eligible for the plan on the last day of the plan year to receive a matching contribution, subject to certain exceptions enumerated in the plan document. Matching contributions are subject to a five-year graduated vesting schedule and can be funded in cash or company stock. We expensed (net of plan forfeitures) $ 63.6 million, $ 59.4 million and $ 53.9 million related to the plan in 2020, 2019 and 2018, respectively. Our board of directors has authorized use of common stock to fund our 2020 employer matching contributions to the 401(k) plan, which we plan to do in February 2021.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Earnings	12 Months Ended
Accumulated Other Comprehensive Earnings	Dec. 31, 2020
Equity [Abstract]
Accumulated Other Comprehensive Earnings	21. Accumulated Other Comprehensive Earnings The after-tax components of our accumulated comprehensive earnings (loss) attributable to controlling interests consist of the following (in millions): Pension Liability Foreign Currency Translation Fair Value of Derivative Instruments Accumulated Comprehensive Earnings (Loss) Balance as of January 1, 2018 $ (43.0 ) $ (521.3 ) $ 8.9 $ (555.4 ) Reclassification to retained earnings of income tax effects related to the TCJA (7.9 ) — 1.3 (6.6 ) Net change in period (10.3 ) (197.7 ) (15.6 ) (223.6 ) Balance as of December 31, 2018 (61.2 ) (719.0 ) (5.4 ) (785.6 ) Cumulative effect of adoption of new accounting standards — — (0.2 ) (0.2 ) Net change in period 4.7 44.2 (22.7 ) 26.2 Balance as of December 31, 2019 (56.5 ) (674.8 ) (28.3 ) (759.6 ) Net change in period 0.4 183.7 (68.1 ) 116.0 Balance as of December 31, 2020 $ (56.1 ) $ (491.1 ) $ (96.4 ) $ (643.6 ) The foreign currency translation in 2020, 2019 and 2018 relates to the net impact of changes in the value of the local currencies relative to the U.S. dollar for our operations in the U.K., Australia, Canada, New Zealand, the Caribbean, India and other non-U.S. locations. During 2020, 2019 and 2018, $6.1 million, $7.0 million and $4.9 million, respectively, of expense related to the pension liability was reclassified from accumulated other comprehensive loss to compensation expense in the statement of earnings. During 2020, 2019 and 2018, $6.3 million of expense, $5.2 million of expense and $5.7 million of income, respectively, related to the fair value of derivative investments, was reclassified from accumulated other comprehensive loss to the statement of earnings. During 2020, 2019 and 2018, no amounts related to foreign currency translation were reclassified from accumulated other comprehensive loss to the statement of earnings.

Quarterly Operating Results (un

Quarterly Operating Results (unaudited)	12 Months Ended
Quarterly Operating Results (unaudited)	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Quarterly Operating Results (unaudited)	22. Quarterly Operating Results (unaudited) Quarterly operating results for 2020 and 2019 were as follows (in millions, except per share data): 1st 2nd 3rd 4th 2020 Total revenues $ 1,866.9 $ 1,584.0 $ 1,849.1 $ 1,703.6 Total expenses 1,510.9 1,412.3 1,639.6 1,569.9 Earnings before income taxes $ 356.0 $ 171.7 $ 209.5 $ 133.7 Net earnings attributable to controlling interests $ 346.3 $ 153.7 $ 176.6 $ 142.2 Basic net earnings per share $ 1.83 $ 0.81 $ 0.92 $ 0.74 Diluted net earnings per share $ 1.79 $ 0.79 $ 0.90 $ 0.72 2019 Total revenues $ 1,990.6 $ 1,657.8 $ 1,825.2 $ 1,721.4 Total expenses 1,668.8 1,552.3 1,710.4 1,637.4 Earnings before income taxes $ 321.8 $ 105.5 $ 114.8 $ 84.0 Net earnings attributable to controlling interests $ 334.1 $ 110.1 $ 126.1 $ 98.5 Basic net earnings per share $ 1.81 $ 0.59 $ 0.68 $ 0.53 Diluted net earnings per share $ 1.77 $ 0.58 $ 0.66 $ 0.51

Segment Information

Segment Information	12 Months Ended
Segment Information	Dec. 31, 2020
Segment Reporting [Abstract]
Segment Information	23. We have three reportable segments: brokerage, risk management and corporate. The brokerage segment is primarily comprised of our retail and wholesale insurance brokerage operations. The brokerage segment generates revenues through commissions paid by underwriting enterprises underwriting enterprises The risk management segment provides contract claim settlement and administration services for enterprises and public entities that choose to self-insure some or all of their property/casualty coverages and for underwriting enterprises that choose to outsource some or all of their property/casualty claims departments. These operations also provide claims management, loss control consulting and insurance property appraisal services. Revenues are principally generated on a negotiated per-claim or per-service fee basis. Our risk management segment also provides risk management consulting services that are recognized as the services are delivered. The corporate segment manages our clean energy and other investments. In addition, the corporate segment reports the financial information related to our debt and other corporate costs, external acquisition-related expenses and the impact of foreign currency translation. Allocations of investment income and certain expenses are based on reasonable assumptions and estimates primarily using revenue, headcount and other information. We allocate the provision for income taxes to the brokerage and risk management segments using the local country statutory rates. Financial information relating to our segments for 2020, 2019 and 2018 is as follows (in millions): Year Ended December 31, 2020 Brokerage Risk Management Corporate Total Revenues: Commissions $ 3,591.9 $ — $ — $ 3,591.9 Fees 1,136.9 821.0 — 1,957.9 Supplemental revenues 221.9 — — 221.9 Contingent revenues 147.0 — — 147.0 Investment income 75.2 0.7 — 75.9 Net losses on divestitures (5.8 ) — — (5.8 ) Revenue from clean coal activities — — 863.5 863.5 Other net losses — — (0.4 ) (0.4 ) Revenues before reimbursements 5,167.1 821.7 863.1 6,851.9 Reimbursements — 151.7 — 151.7 Total revenues 5,167.1 973.4 863.1 7,003.6 Compensation 2,882.5 517.5 66.5 3,466.5 Operating 687.2 162.6 56.7 906.5 Reimbursements — 151.7 — 151.7 Cost of revenues from clean coal activities — — 882.1 882.1 Interest — — 196.4 196.4 Depreciation 73.5 49.4 22.2 145.1 Amortization 411.3 6.0 — 417.3 Change in estimated acquisition earnout payables (29.7 ) (3.2 ) — (32.9 ) Total expenses 4,024.8 884.0 1,223.9 6,132.7 Earnings (loss) before income taxes 1,142.3 89.4 (360.8 ) 870.9 Provision (benefit) for income taxes 276.3 22.5 (286.0 ) 12.8 Net earnings (loss) 866.0 66.9 (74.8 ) 858.1 Net earnings attributable to noncontrolling interests 4.9 — 34.4 39.3 Net earnings (loss) attributable to controlling interests $ 861.1 $ 66.9 $ (109.2 ) $ 818.8 Net foreign exchange loss $ (2.6 ) $ (0.1 ) $ (0.2 ) $ (2.9 ) Revenues: United States $ 3,369.4 $ 816.4 $ 863.1 $ 5,048.9 United Kingdom 993.7 40.7 — 1,034.4 Australia 216.1 98.4 — 314.5 Canada 243.8 5.3 — 249.1 New Zealand 141.8 12.6 — 154.4 Other foreign 202.3 — — 202.3 Total revenues $ 5,167.1 $ 973.4 $ 863.1 $ 7,003.6 At December 31, 2020 Identifiable assets: United States $ 8,897.9 $ 716.2 $ 2,172.2 $ 11,786.3 United Kingdom 6,135.1 139.2 — 6,274.3 Australia 1,373.3 89.6 — 1,462.9 Canada 1,053.6 4.8 — 1,058.4 New Zealand 766.0 24.1 — 790.1 Other foreign 959.4 — — 959.4 Total identifiable assets $ 19,185.3 $ 973.9 $ 2,172.2 $ 22,331.4 Goodwill - net $ 6,053.6 $ 70.5 $ 2.9 $ 6,127.0 Amortizable intangible assets - net 2,376.3 23.6 — 2,399.9 Year Ended December 31, 2019 Brokerage Risk Management Corporate Total Revenues: Commissions $ 3,320.6 $ — $ — $ 3,320.6 Fees 1,074.2 836.9 — 1,911.1 Supplemental revenues 210.5 — — 210.5 Contingent revenues 135.6 — — 135.6 Investment income 85.3 1.6 — 86.9 Net gains on divestitures 75.3 — — 75.3 Revenue from clean coal activities — — 1,319.3 1,319.3 Other net losses — — (2.9 ) (2.9 ) Revenues before reimbursements 4,901.5 838.5 1,316.4 7,056.4 Reimbursements — 138.6 — 138.6 Total revenues 4,901.5 977.1 1,316.4 7,195.0 Compensation 2,745.9 515.7 77.9 3,339.5 Operating 796.5 184.9 87.1 1,068.5 Reimbursements — 138.6 — 138.6 Cost of revenues from clean coal activities — — 1,352.8 1,352.8 Interest — — 179.8 179.8 Depreciation 66.6 46.2 27.6 140.4 Amortization 329.1 4.9 — 334.0 Change in estimated acquisition earnout payables 16.9 (1.6 ) — 15.3 Total expenses 3,955.0 888.7 1,725.2 6,568.9 Earnings (loss) before income taxes 946.5 88.4 (408.8 ) 626.1 Provision (benefit) for income taxes 229.2 22.2 (341.1 ) (89.7 ) Net earnings (loss) 717.3 66.2 (67.7 ) 715.8 Net earnings attributable to noncontrolling interests 17.2 — 29.8 47.0 Net earnings (loss) attributable to controlling interests $ 700.1 $ 66.2 $ (97.5 ) $ 668.8 Net foreign exchange loss $ (1.0 ) $ (0.1 ) $ (5.6 ) $ (6.7 ) Revenues: United States $ 3,234.3 $ 828.4 $ 1,316.4 $ 5,379.1 United Kingdom 921.8 41.6 — 963.4 Australia 211.3 87.3 — 298.6 Canada 221.4 4.6 — 226.0 New Zealand 145.6 15.2 — 160.8 Other foreign 167.1 — — 167.1 Total revenues $ 4,901.5 $ 977.1 $ 1,316.4 $ 7,195.0 At December 31, 2019 Identifiable assets: United States $ 8,132.3 $ 655.6 $ 1,994.8 $ 10,782.7 United Kingdom 4,964.5 126.6 — 5,091.1 Australia 1,217.9 90.0 — 1,307.9 Canada 913.6 3.1 — 916.7 New Zealand 695.9 22.8 — 718.7 Other foreign 817.7 — — 817.7 Total identifiable assets $ 16,741.9 $ 898.1 $ 1,994.8 $ 19,634.8 Goodwill - net $ 5,548.9 $ 66.6 $ 3.0 $ 5,618.5 Amortizable intangible assets - net 2,289.9 28.8 — 2,318.7 Year Ended December 31, 2018 Brokerage Risk Management Corporate Total Revenues: Commissions $ 2,920.7 $ — $ — $ 2,920.7 Fees 958.5 797.8 — 1,756.3 Supplemental revenues 189.9 — — 189.9 Contingent revenues 98.0 — — 98.0 Investment income 69.6 0.5 — 70.1 Net gains on divestitures 10.2 — — 10.2 Revenue from clean coal activities — — 1,746.3 1,746.3 Other net gains — — 0.9 0.9 Revenues before reimbursements 4,246.9 798.3 1,747.2 6,792.4 Reimbursements — 141.6 — 141.6 Total revenues 4,246.9 939.9 1,747.2 6,934.0 Compensation 2,447.1 489.7 89.5 3,026.3 Operating 673.5 174.6 55.6 903.7 Reimbursements — 141.6 — 141.6 Cost of revenues from clean coal activities — — 1,816.0 1,816.0 Interest — — 138.4 138.4 Depreciation 60.9 38.7 28.2 127.8 Amortization 286.9 4.3 — 291.2 Change in estimated acquisition earnout payables 14.3 (4.7 ) — 9.6 Total expenses 3,482.7 844.2 2,127.7 6,454.6 Earnings (loss) before income taxes 764.2 95.7 (380.5 ) 479.4 Provision (benefit) for income taxes 191.0 25.3 (412.8 ) (196.5 ) Net earnings 573.2 70.4 32.3 675.9 Net earnings attributable to noncontrolling interests 10.7 - 31.7 42.4 Net earnings attributable to controlling interests $ 562.5 $ 70.4 $ 0.6 $ 633.5 Net foreign exchange gain $ - $ - $ 2.9 $ 2.9 Revenues: United States $ 2,840.9 $ 789.7 $ 1,747.2 $ 5,377.8 United Kingdom 738.5 35.4 — 773.9 Australia 195.9 94.7 — 290.6 Canada 181.1 4.3 — 185.4 New Zealand 141.7 15.8 — 157.5 Other foreign 148.8 — — 148.8 Total revenues $ 4,246.9 $ 939.9 $ 1,747.2 $ 6,934.0 At December 31, 2018 Identifiable assets: United States $ 6,865.4 $ 571.4 $ 1,800.8 $ 9,237.6 United Kingdom 3,758.5 103.8 — 3,862.3 Australia 1,096.1 47.2 — 1,143.3 Canada 783.1 4.4 — 787.5 New Zealand 688.5 21.3 — 709.8 Other foreign 593.5 — — 593.5 Total identifiable assets $ 13,785.1 $ 748.1 $ 1,800.8 $ 16,334.0 Goodwill - net $ 4,573.6 $ 49.3 $ 2.7 $ 4,625.6 Amortizable intangible assets - net 1,753.7 19.3 — 1,773.0

Schedule II. Valuation and Qual

Schedule II. Valuation and Qualifying Accounts	12 Months Ended
Schedule II. Valuation and Qualifying Accounts	Dec. 31, 2020
Valuation And Qualifying Accounts [Abstract]
Schedule II. Valuation and Qualifying Accounts	Schedule II Arthur J. Gallagher & Co. Valuation and Qualifying Accounts Balance at Beginning of Year Amounts Recorded in Earnings Adjustments Balance at End of Year (In millions) Year ended December 31, 2020 Allowance for doubtful accounts $ 8.7 $ 6.6 $ (5.2 ) (1) $ 10.1 Allowance for estimated policy cancellations 8.3 4.1 (2.5 ) (2) 9.9 Valuation allowance for deferred tax assets 80.5 14.4 — 94.9 Accumulated amortization of expiration lists, non-compete agreements and trade names 2,087.5 417.3 32.2 (3) 2,537.0 Year ended December 31, 2019 Allowance for doubtful accounts $ 10.0 $ 4.2 $ (5.5 ) (1) $ 8.7 Allowance for estimated policy cancellations 7.8 0.5 — (2) 8.3 Valuation allowance for deferred tax assets 67.4 13.1 — 80.5 Accumulated amortization of expiration lists, non-compete agreements and trade names 1,750.4 334.0 3.1 (3) 2,087.5 Year ended December 31, 2018 Allowance for doubtful accounts $ 13.5 $ 5.8 $ (9.3 ) (1) $ 10.0 Allowance for estimated policy cancellations 7.4 (1.2 ) 1.6 (2) 7.8 Valuation allowance for deferred tax assets 79.1 (11.7 ) — 67.4 Accumulated amortization of expiration lists, non-compete agreements and trade names 1,490.7 291.2 (31.5 ) (3) 1,750.4 (1) Net activity of bad debt write offs and recoveries and acquired businesses. (2) Additions to allowance related to acquired businesses. (3) Elimination of fully amortized expiration lists, non-compete agreements and trade names, intangible asset/amortization reclassifications and disposal of acquired businesses.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2020
Accounting Policies [Abstract]
Nature of Operations	Nature of Operations Arthur J. Gallagher & Co. and its subsidiaries, collectively referred to herein as we, our, us or the company, provide insurance brokerage, consulting and third party claims settlement and administration services to both domestic and international entities. We have three reportable segments: brokerage, risk management and corporate. Our brokers, agents and administrators act as intermediaries between and our clients. Our brokerage segment operations provide brokerage and consulting services to companies and entities of all types, including commercial, not-for-profit, public entities, and, to a lesser extent, individuals, in the areas of insurance placement, risk of loss management, and management of employer sponsored benefit programs. Our risk management segment operations provide contract claim settlement, claim administration, loss control services and risk management consulting for commercial, not‑for‑profit, captive and public entities, and various other organizations that choose to self-insure property/casualty coverages or choose to use a third-party claims management organization rather than the claim services provided by underwriting enterprises. The corporate segment reports the financial information related to our debt and other corporate costs, clean energy investments, external acquisition-related expenses and the impact of foreign currency translation. Clean energy investments consist of our investments in limited liability companies that own 35 commercial clean coal production facilities producing refined coal using Chem-Mod LLC’s proprietary technologies. We believe these operations produce refined coal that qualifies for tax credits under IRC Section 45. We do not assume underwriting risk on a net basis, other than with respect to de minimis amounts necessary to provide minimum or regulatory capital to organize captives, pools, specialized underwriters or risk-retention groups. Rather, capital necessary for covering losses is provided by underwriting enterprises. Investment income and other revenues are primarily generated from our premium financing operations, our invested cash and restricted cash we hold on behalf of our clients, as well as clean energy investments. In addition, our share of the net earnings related to partially owned entities that are accounted for using the equity method is included in investment income. We are headquartered in Rolling Meadows, Illinois, have operations in 49 countries and offer client-service capabilities in more than 150 countries globally through a network of correspondent insurance brokers and consultants.
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include our accounts and all of our majority-owned subsidiaries (50% or greater ownership). Substantially all of our investments in partially owned entities in which our ownership is less than 50% are accounted for using the equity method based on the legal form of our ownership interest and the applicable ownership percentage of the entity. However, in situations where a less than 50%-owned investment has been determined to be a VIE and we are deemed to be the primary beneficiary in accordance with the variable interest model of consolidation, we will consolidate the investment into our consolidated financial statements. For partially owned entities accounted for using the equity method, our share of the net earnings of these entities is included in consolidated net earnings. All material intercompany accounts and transactions have been eliminated in consolidation. In the preparation of our consolidated financial statements as of December 31, 2020, management evaluated all material subsequent events or transactions that occurred after the balance sheet date through the date on which the financial statements were issued for potential recognition and/or disclosure in the notes therein.
Use of Estimates	Use of Estimates The preparation of our consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. These accounting principles require us to make estimates and assumptions that affect the reported amounts of assets and liabilities and revenues and expenses, and the disclosure of contingent assets and liabilities at the date of our consolidated financial statements. We periodically evaluate our estimates and assumptions, including those relating to the valuation of goodwill and other intangible assets, right-of-use assets, investments (including our IRC Section 45 investments), income taxes, revenue recognition, deferred costs, stock-based compensation, claims handling obligations, retirement plans, litigation and contingencies. We base our estimates on historical experience and various assumptions that we believe to be reasonable based on specific circumstances. Such estimates and assumptions could change in the future as more information becomes known, which could impact the amounts reported and disclosed herein.
Revenue Recognition	Revenue Recognition Our revenues are derived from commissions and fees as primarily specified in a written contract, or unwritten business understanding, with our clients or underwriting enterprises. We also recognize investment income over time from our invested assets and invested assets we hold on behalf of our clients or underwriting enterprises.
Brokerage Segment	BROKERAGE SEGMENT Our brokerage segment generates revenues by: (i) Identifying, negotiating and placing all forms of insurance or reinsurance coverage, as well as providing risk-shifting, risk-sharing and risk-mitigation consulting services, principally related to property/casualty, life, health, welfare and disability insurance. We also provide these services through, or in conjunction with, other unrelated agents and brokers, consultants and management advisors. (ii) Acting as an agent or broker for multiple underwriting enterprises by providing services such as sales, marketing, selecting, negotiating, underwriting, servicing and placing insurance coverage on their behalf. (iii) Providing consulting services related to health and welfare benefits, voluntary benefits, executive benefits, compensation, retirement planning, institutional investment and fiduciary, actuarial, compliance, private insurance exchange, human resource technology, communications and benefits administration. (iv) Providing management and administrative services to captives, pools, risk-retention groups, healthcare exchanges, small underwriting enterprises, such as accounting, claims and loss processing assistance, feasibility studies, actuarial studies, data analytics and other administrative services. The vast majority of our brokerage contracts and service understandings are for a period of one year or less. Commissions and fees The primary source of revenues for our brokerage services is commissions from underwriting enterprises, based on a percentage of premiums paid by our clients, or fees received from clients based on an agreed level of service usually in lieu of commissions. These commissions and fees revenues are substantially recognized at a point in time on the effective date of the associated policies when control of the policy transfers to the client, as well as deferring certain revenues to reflect delivery of services over the contract period. Commissions are fixed at the contract effective date and generally are based on a percentage of premiums for insurance coverage or employee headcount for employer sponsored benefit plans. Commissions depend upon a large number of factors, including the type of risk being placed, the particular underwriting enterprise’s demand, the expected loss experience of the particular risk of coverage, and historical benchmarks surrounding the level of effort necessary for us to place and service the insurance contract. Rather than being tied to the amount of premiums, fees are most often based on an expected level of effort to provide our services. Whether we are paid a commission or a fee, the vast majority of our services are associated with the placement of an insurance (or insurance-like) contract. Accordingly, we recognize approximately 80% of our commission and fee revenues on the effective date of the underlying insurance contract. The amount of revenue we recognize is based on our costs to provide our services up and through that effective date, including an appropriate estimate of our profit margin on a portfolio basis (a practical expedient as defined in Topic 606). Based on the proportion of additional services we provide in each period after the effective date of the insurance contract, including an appropriate estimate of our profit margin, we recognize approximately 15% of our commission and fee revenues in the first three months, and the remaining 5% thereafter. These periods may be different than the underlying premium payment patterns of the insurance contracts, but the vast majority of our services are fully provided within one year of the insurance contract effective date. For consulting and advisory services, we recognize our revenue in the period in which we provide the service or advice. For management and administrative services, our revenue is recognized ratably over the contract period consistent with the performance of our obligations, mostly over an annual term. Supplemental revenues Certain underwriting enterprises may pay us additional revenues for the volume of premium placed with them and for insights into our sales pipeline, our sales capabilities or our risk selection knowledge. These amounts are in excess of the commission and fee revenues discussed above, and not all business we place with underwriting enterprises is eligible for supplemental revenues. Unlike contingent revenues, discussed below, these revenues are primarily a fixed amount or fixed percentage of premium of the underlying eligible insurance contracts. For supplemental revenue contracts based on a fixed percentage of premium, our obligation to the underwriting enterprise is substantially completed upon the effective date of the underlying insurance contract and revenue is fully earned at that time. For supplemental revenue contracts based on a fixed amount, revenue is recognized ratably over the contract period consistent with the performance of our obligations, almost always over an annual term. We receive these revenues on a quarterly or annual basis. Contingent revenues Certain underwriting enterprises may pay us additional revenues for our sales capabilities, our risk selection knowledge, or our administrative efficiencies. These amounts are in excess of the commission or fee revenues discussed above, and not all business we place with participating underwriting enterprises is eligible for contingent revenues. Unlike supplemental revenues, also discussed above, these revenues are variable, generally based on growth, the loss experience of the underlying insurance contracts, and/or our efficiency in processing the business. We generally operate under calendar year contracts, but we do not receive these revenues from the underwriting enterprises until the following calendar year, generally in the first and second quarters, after verification of the performance indicators outlined in the contracts. Accordingly, during each reporting period, we must make our best estimate of amounts we have earned using historical averages and other factors to project such revenues. We base our estimates each period on a contract-by-contract basis where available. In certain cases, it is impractical to assess a very large number of smaller contingent revenue contracts, so we use a historical portfolio estimate in aggregate (a practical expedient as defined in Topic 606). Because our expectation of the ultimate contingent revenue amounts to be earned can vary from period to period, especially in contracts sensitive to loss ratios, our estimates might change significantly from quarter to quarter. For example, in circumstances where our revenues are dependent on a full calendar year loss ratio, adverse loss experience in the fourth quarter could not only negate revenue earnings in the fourth quarter, but also trigger the need to reverse revenues previously recognized during the prior quarters. Variable consideration is recognized when we conclude, based on all the facts and information available at the reporting date, that it is probable that a significant revenue reversal will not occur in future periods. Sub-b rokerage costs Sub-brokerage costs are excluded from our gross revenues in our determination of total revenues. Sub-brokerage cost represents commissions paid to sub-brokers related to the placement of certain business by our brokerage segment operations. We recognize this contra revenue
Risk Management Segment	RISK MANAGEMENT SEGMENT Revenues for our risk management segment are comprised of fees generally negotiated (i) on a per-claim basis, (ii) on a cost‑plus basis, or (iii) as performance-based fees. We also provide risk management consulting services that are recognized as the services are delivered. Per-claim fees Where we operate under a contract with our fee established on a per-claim basis, our obligation is to process claims for a term specified within the contract. Because it is impractical to recognize our revenues on an individual claim-by-claim basis, we recognize revenue plus an appropriate estimate of our profit margin on a portfolio basis by grouping claims with similar characteristics (a practical expedient as defined in Topic 606). We apply actuarially-determined, historical-based patterns to determine our future service obligations, without applying a present value discount. Cost-plus fees Where we provide services and generate revenues on a cost-plus basis, we recognize revenue over the contract period consistent with the performance of our obligations. Performance-based fees Certain clients pay us additional fee revenues for our efficiency in managing claims or on the basis of claim outcome effectiveness. These amounts are in excess of the fee revenues discussed above. These revenues are variable, generally based on performance metrics set forth in the underlying contracts. We generally operate under multi-year contracts with fiscal year measurement periods. We do not receive these fees, if earned, until the following year after verification of the performance metrics outlined in the contracts. Each period we base our estimates on a contract-by-contract basis. We must make our best estimate of amounts we have earned using historical averages and other factors to project such revenues. Variable consideration is recognized when we conclude that is it probable that a significant revenue reversal will not occur in future periods. Reimbursements Reimbursements represent amounts received from clients reimbursing us for certain third-party costs associated with providing our claims management services. In certain service partner relationships, we are considered a principal because we direct the third party, control the specified service and combine the services provided into an integrated solution. Given this principal relationship, we are required to recognize revenue gross and service partner vendor fees in the operating expense in our consolidated statement of earnings.
Deferred Costs	Deferred Costs We incur costs to provide brokerage and risk management services. Those costs are either (i) costs to obtain a contract or (ii) costs to fulfill such contract, or (iii) all other costs. (i) Costs to obtain - we incur costs to obtain a contract with a client. Those costs would not have been incurred if the contract had not been obtained. Almost all of our costs to obtain are incurred prior to, or on, the effective date of the contract and consist primarily of incentive compensation we pay to our production employees. Our costs to obtain are expensed as incurred as described in Note 4 to these consolidated financial statements. (ii) Costs to fulfill - we incur costs to fulfill a contract (or anticipated contract) with a client. Those costs are incurred prior to the effective date of the contract and relate to fulfilling our primary placement obligations to our clients. Our costs to fulfill prior to the effective date are capitalized and amortized on the effective date. These fulfillment activities include collecting underwriting information from our client, assessing their insurance needs and negotiating their placement with one or more underwriting enterprises. The majority of costs that we incur relate to compensation and benefits of our client service employees. Costs incurred during preplacement activities are expected to be recovered in the future. If the capitalized costs are no longer deemed to be recoverable, then they would be expensed. (iii) Other costs that are not costs to obtain or fulfill are expensed as incurred. Examples include other operating costs such as rent, utilities, management costs, overhead costs, legal and other professional fees, technology costs, insurance related costs, communication and advertising, and travel and entertainment. Depreciation, amortization and change in estimated acquisition earnout payable are expensed as incurred.
Investment income	Investment income Investment income primarily includes interest and dividend income (including interest income from our premium financing operations), which is accrued as it is earned. Net gains on divestitures represent one-time gains related to sales of brokerage related businesses, which are primarily recognized on a cash received basis. Revenues from clean coal activities include revenues from consolidated clean coal production plants, royalty income from clean coal licenses and income (loss) related to unconsolidated clean coal production plants, all of which are recognized as earned. Revenues from consolidated clean coal production plants represent sales of refined coal. Royalty income from clean coal licenses represents fee income related to the use of clean coal technologies. Income (loss) from unconsolidated clean coal production plants includes losses related to our equity portion of the pretax results of the clean coal production plants.
Earnings per Share	Earnings per Share Basic net earnings per share is computed by dividing net earnings by the weighted average number of common shares outstanding during the reporting period. Diluted net earnings per share is computed by dividing net earnings by the weighted average number of common and common equivalent shares outstanding during the reporting period. Common equivalent shares include incremental shares from dilutive stock options, which are calculated from the date of grant under the treasury stock method using the average market price for the period.
Cash and Cash Equivalents	Cash and Cash Equivalents Short-term investments, consisting principally of cash and money market accounts that have average maturities of 90 days or less, are considered cash equivalents.
Restricted Cash	Restricted Cash In our capacity as an insurance broker, we collect premiums from insureds and, after deducting our commissions and/or fees, remit these premiums to underwriting enterprises underwriting enterprises Related to our third party administration business and in certain of our brokerage operations, we are responsible for client claim funds that we hold in a fiduciary capacity. We do not earn any interest income on the funds held. These client funds have been included in restricted cash, along with a corresponding liability in premiums payable to underwriting enterprises
Premiums and fees receivable	Premiums and fees receivable Premiums and fees receivable in the accompanying consolidated balance sheet are net of allowances for estimated policy cancellations and doubtful accounts. The allowance for estimated policy cancellations was $9.9 million and $8.3 million at December 31, 2020 and 2019, respectively, which represents a reserve for future reversals in commission and fee revenues related to the potential cancellation of client insurance policies that were in force as of each year end. The allowance for doubtful accounts was $10.1 million and $8.7 million at December 31, 2020 and 2019, respectively. We establish the allowance for estimated policy cancellations through a charge to revenues and the allowance for doubtful accounts through a charge to operating expenses. Both of these allowances are based on estimates and assumptions using historical data to project future experience. Such estimates and assumptions could change in the future as more information becomes known which could impact the amounts reported and disclosed herein. We periodically review the adequacy of these allowances and make adjustments as necessary.
Derivative Instruments	Derivative Instruments We are exposed to market risks, including changes in foreign currency exchange rates and interest rates. To manage the risk related to these exposures, we enter into various derivative instruments that reduce these risks by creating offsetting exposures. In the normal course of business, we are exposed to the impact of foreign currency fluctuations that impact our results of operations and cash flows. We utilize a foreign currency risk management program involving foreign currency derivatives that consist of several monthly put/call options designed to hedge a portion of our future foreign currency disbursements through various future payment dates. To mitigate the counterparty credit risk we only enter into contracts with major financial institutions based upon their credit ratings and other factors. These derivative instrument contracts are cash flow hedges that qualify for hedge accounting and primarily hedge against fluctuations between changes in the GBP and Indian Rupee versus the U.S. dollar. Changes in fair value of the derivative instruments are reflected in other comprehensive earnings in the accompanying consolidated balance sheet. The impact of the hedge at maturity is recognized in the income statement as a component of investment income, compensation and operating expenses depending on the nature of the hedged item. We enter into various long-term debt agreements. We use interest rate derivatives, typically swaps, to reduce our exposure to the effects of interest rate fluctuations on the forecasted interest rates for up to three years into the future. These derivative instrument contracts are periodically monitored for hedge ineffectiveness, the amount of which has not been material to the accompanying consolidated financial statements. We do not use derivatives for trading or speculative purposes.
Premium Financing	Premium Financing Seven subsidiaries of the brokerage segment make short-term loans (generally with terms of twelve months or less) to our clients to finance premiums. These premium financing contracts are structured to minimize potential bad debt expense to us. Such receivables are generally considered delinquent after seven days of the payment due date. In normal course, insurance policies are cancelled within one month of the contractual payment due date if the payment remains delinquent. We recognize interest income as it is earned over the life of the contract using the “level-yield” method. Unearned interest related to contracts receivable is included in the receivable balance in the accompanying consolidated balance sheet. The outstanding loan receivable balance was $442.7 million and $388.1 million at December 31, 2020 and 2019, respectively.
Fixed Assets	Fixed Assets We carry fixed assets at cost, less accumulated depreciation, in the accompanying consolidated balance sheet. We periodically review long-lived assets for impairment whenever events or changes in business circumstances indicate that the carrying value of the assets may not be recoverable. Under those circumstances, if the fair value were less than the carrying amount of the asset, we would recognize a loss for the difference. Depreciation for fixed assets is computed using the straight-line method over the following estimated useful lives: Useful Life Office equipment Three to ten years Furniture and fixtures Three to ten years Computer equipment Three to five years Building Fifteen to forty years Software Three to five years Refined fuel plants Ten years Leasehold improvements Shorter of the lease term or useful life of the asset
Intangible Assets	Intangible Assets Intangible assets represent the excess of cost over the estimated fair value of net tangible assets of acquired businesses. Our primary intangible assets are classified as either goodwill, expiration lists, non-compete agreements or trade names. Expiration lists, non-compete agreements and trade names are amortized using the straight-line method over their estimated useful lives (two to fifteen years for expiration lists, two to six years for non-compete agreements and two to fifteen years for trade names), while goodwill is not subject to amortization. The establishment of goodwill, expiration lists, non-compete agreements and trade names and the determination of estimated useful lives are primarily based on valuations we receive from qualified independent appraisers. The calculations of these amounts are based on estimates and assumptions using historical and projected financial information and recognized valuation methods. Different estimates or assumptions could produce different results. We carry identifiable intangible assets at cost, less accumulated amortization, in the accompanying consolidated balance sheet. We review all of our intangible assets for impairment periodically (at least annually for goodwill) and whenever events or changes in business circumstances indicate that the carrying value of the assets may not be recoverable. We perform such impairment reviews at the division (i.e., reporting unit) level with respect to goodwill and at the business unit level for amortizable intangible assets. While goodwill is not amortizable, it is tested for impairment at least annually in the fourth quarter, and more frequently if there are indicators of impairment or whenever business circumstances suggest that the carrying value of goodwill may not be recoverable. We may initially perform a qualitative analysis to determine if it is more likely than not that the goodwill balance is impaired. If a qualitative assessment is not performed or if a The carrying value of amortizable intangible assets attributable to each business or asset group is periodically reviewed by management to determine if there are events or changes in circumstances that would indicate that its carrying amount may not be recoverable. Accordingly, if there are any such changes in circumstances during the year, we assess the carrying value of the amortizable intangible assets by considering the estimated future undiscounted cash flows generated by the corresponding business or asset group. Any impairment identified through this assessment may require that the carrying value of related amortizable intangible assets be adjusted and charged against current period earnings as a component of amortization expense. Based on the results of impairment reviews in 2020, 2019 and 2018, we wrote off $51.7 million, $0.1 million and $10.6 million, respectively, of amortizable intangible assets primarily related to prior year acquisitions of our brokerage and risk management segments, which is included in amortization expense in the accompanying consolidated statement of earnings.
Income Taxes	Income Taxes Our tax rate reflects the statutory tax rates applicable to our taxable earnings and tax planning in the various jurisdictions in which we operate. Significant judgment is required in determining the annual effective tax rate and in evaluating uncertain tax positions. We report a liability for unrecognized tax benefits resulting from uncertain tax positions taken or expected to be taken in our tax return. We evaluate our tax positions using a two-step process. The first step involves recognition. We determine whether it is more likely than not that a tax position will be sustained upon tax examination based solely on the technical merits of the position. The technical merits of a tax position are derived from both statutory and judicial authority (legislation and statutes, legislative intent, regulations, rulings and case law) and their applicability to the facts and circumstances of the position. If a tax position does not meet the “more likely than not” recognition threshold, we do not recognize the benefit of that position in the financial statements. The second step is measurement. A tax position that meets the “more likely than not” recognition threshold is measured to determine the amount of benefit to recognize in the financial statements. The tax position is measured as the largest amount of benefit that has a likelihood of greater than 50% of being realized upon ultimate resolution with a taxing authority. Uncertain tax positions are measured based upon the facts and circumstances that exist at each reporting period and involve significant management judgment. Subsequent changes in judgment based upon new information may lead to changes in recognition, derecognition and measurement. Adjustments may result, for example, upon resolution of an issue with the taxing authorities, or expiration of a statute of limitations barring an assessment for an issue. We recognize interest and penalties, if any, related to unrecognized tax benefits in our provision for income taxes. Tax law requires certain items to be included in our tax returns at different times than such items are reflected in the financial statements. As a result, the annual tax expense reflected in our consolidated statements of earnings is different than that reported in our tax returns. Some of these differences are permanent, such as expenses that are not deductible in our tax returns, and some differences are temporary and reverse over time, such as depreciation expense and amortization expense deductible for income tax purposes. Temporary differences create deferred tax assets and liabilities. Deferred tax liabilities generally represent tax expense recognized in the financial statements for which a tax payment has been deferred, or expense which has been deducted in the tax return but has not yet been recognized in the financial statements. Deferred tax assets generally represent items that can be used as a tax deduction or credit in tax returns in future years for which a benefit has already been recorded in the financial statements. We establish or adjust valuation allowances for deferred tax assets when we estimate that it is more likely than not that future taxable income will be insufficient to fully use a deduction or credit in a specific jurisdiction. In assessing the need for the recognition of a valuation allowance for deferred tax assets, we consider whether it is more likely than not that some portion, or all, of the deferred tax assets will not be realized and adjust the valuation allowance accordingly. We evaluate all significant available positive and negative evidence as part of our analysis. Negative evidence includes the existence of losses in recent years. Positive evidence includes the forecast of future taxable income by jurisdiction, tax-planning strategies that would result in the realization of deferred tax assets and the presence of taxable income in prior carryback years. The underlying assumptions we use in forecasting future taxable income require significant judgment and take into account our recent performance. Such estimates and assumptions could change in the future as more information becomes known which could impact the amounts reported and disclosed herein. The ultimate realization of deferred tax assets depends on the generation of future taxable income during the periods in which temporary differences are deductible or creditable.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Fair value accounting establishes a framework for measuring fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (i.e., an exit price). This framework includes a fair value hierarchy that prioritizes the inputs to the valuation technique used to measure fair value. The classification of a financial instrument within the valuation hierarchy is based upon the transparency of inputs to the valuation of an asset or liability on the measurement date. The three levels of the hierarchy in order of priority of inputs to the valuation technique are defined as follows: • Level 1 - Valuations are based on unadjusted quoted prices in active markets for identical financial instruments; • Level 2 - Valuations are based on quoted market prices, other than quoted prices included in Level 1, in markets that are not active or on inputs that are observable either directly or indirectly for the full term of the financial instrument; and • Level 3 - Valuations are based on pricing or valuation techniques that require inputs that are both unobservable and significant to the overall fair value measurement of the financial instrument. Such inputs may reflect management’s own assumptions about the assumptions a market participant would use in pricing the financial instrument. The level in the fair value hierarchy within which the fair value measurement is classified is determined based on the lowest level input that is significant to the fair value measure in its entirety. The carrying amounts of financial assets and liabilities reported in the accompanying consolidated balance sheet for cash and cash equivalents, restricted cash, premiums and fees receivable, other current assets, premiums payable to underwriting enterprises
Litigation	Litigation We are the defendant in various legal actions related to claims, lawsuits and proceedings incident to the nature of our business. We record liabilities for loss contingencies, including legal costs (such as fees and expenses of external lawyers and other service providers) to be incurred, when it is probable that a liability has been incurred on or before the balance sheet date and the amount of the liability can be reasonably estimated. We do not discount such contingent liabilities. To the extent recovery of such losses and legal costs is probable under our insurance programs, we record estimated recoveries concurrently with the losses recognized. Significant management judgment is required to estimate the amounts of such contingent liabilities and the related insurance recoveries. In order to assess our potential liability, we analyze our litigation exposure based on available information, including consultation with outside counsel handling the defense of these matters. As these liabilities are uncertain by their nature, the recorded amounts may change due to a variety of different factors, including new developments in, or changes in approach, such as changing the settlement strategy as applicable to each matter.
Retention bonus arrangements	Retention bonus arrangements In connection with the hiring and retention of both new talent and experienced personnel, including our senior management, brokers and other key personnel, we have entered into various agreements with key employees setting up the conditions for the cash payment of certain retention bonuses. These bonuses are an incentive for these employees to remain with the company, for a fixed period of time, to allow us to capitalize on their knowledge and experience. We have various forms of retention bonus arrangements; some are paid up front and some are paid at the end of the term, but all are contingent upon successfully completing a minimum period of employment. A retention bonus that is paid to an employee upfront that is contingent on a certain minimum period of employment, will be initially classified as a prepaid asset and amortized to compensation expense as the future services are rendered over the duration of the stay period. A retention bonus that is paid to an employee at the end of the term that is contingent on a certain minimum period of employment , will be accrued as a liability through compensation expense as the future services are rendered over the duration of the stay period. If an employee leaves prior to the require d time frame to earn the retention bonus outright , then all or any portion that is ultimately unearned or refundable , and recovered by the company if prepaid , is forfeited and reverse d through compensation expense .
Stock-Based Compensation	Stock-Based Compensation We have several employee equity-settled and cash-settled share-based compensation plans. Equity-settled share-based payments to employees include grants of stock options, performance stock units and restricted stock units and are measured based on estimated grant date fair value. We have elected to use the Black-Scholes option pricing model to determine the fair value of stock options on the dates of grant. Performance stock units are measured on the probable outcome of the performance conditions applicable to each grant. Restricted stock units are measured based on the fair market values of the underlying stock on the dates of grant. Shares are issued on the vesting dates net of the minimum statutory tax withholding requirements, as applicable, to be paid by us on behalf of our employees. As a result, the actual number of shares issued will be fewer than the actual number of performance stock units and restricted stock units outstanding. Furthermore, we record the liability for withholding amounts to be paid by us as a reduction to additional paid-in capital when paid. Cash-settled share-based payments to employees include awards under our Performance Unit Program and stock appreciation rights. The fair value of the amount payable to employees in respect of cash-settled share-based payments is recognized as compensation expense, with a corresponding increase in liabilities, over the vesting period. The liability is remeasured at each reporting date and at settlement date. Any changes in fair value of the liability are recognized as compensation expense. We recognize share-based compensation expense over the requisite service period for awards expected to ultimately vest. Forfeitures are estimated on the date of grant and revised if actual or expected forfeiture activity differs from original estimates.
Employee Stock Purchase Plan	Employee Stock Purchase Plan We have an employee stock purchase plan (which we refer to as the ESPP), under which the sale of 8.0 million shares of our common stock has been authorized. Eligible employees may contribute up to 15% of their compensation towards the quarterly purchase of our common stock at a purchase price equal to 95% of the lesser of the fair market value of our common stock on the first business day or the last business day of the quarterly offering period. Eligible employees may annually purchase shares of our common stock with an aggregate fair market value of up to $25,000 (measured as of the first day of each quarterly offering period of each calendar year), provided that no employee may purchase more than 2,000 shares of our common stock under the ESPP during any calendar year. At December 31, 2020, 6.0 million shares of our common stock was reserved for future issuance under the ESPP.
Defined Benefit Pension and Other Postretirement Plans	Defined Benefit Pension and Other Postretirement Plans We r ecognize in our consolidated balance sheet, an asset for our defined benefit postretirement plans’ overfunded status or a liability for our plans’ underfunded status. We recognize changes in the funded status of our defined benefit postretirement plans in comprehensive earnings in the year in which the changes occur. We use December 31 as the measurement date for our plans’ assets and benefit obligations. See Note 13 for additional information required to be disclosed related to our defined benefit postretirement plans

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
Summary of Significant Accounting Policies (Tables)	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Estimated Useful Life of Fixed Assets	Depreciation for fixed assets is computed using the straight-line method over the following estimated useful lives: Useful Life Office equipment Three to ten years Furniture and fixtures Three to ten years Computer equipment Three to five years Building Fifteen to forty years Software Three to five years Refined fuel plants Ten years Leasehold improvements Shorter of the lease term or useful life of the asset

Business Combinations (Tables)

Business Combinations (Tables)	12 Months Ended
Business Combinations (Tables)	Dec. 31, 2020
Business Combinations [Abstract]
Acquisition Method for Recording Business Combinations	During 2020, we acquired substantially all of the net assets of the following firms in exchange for our common stock and/or cash. These acquisitions have been accounted for using the acquisition method for recording business combinations (in millions, except share data): Name and Effective Date of Acquisition Common Shares Issued Common Share Value Cash Paid Accrued Liability Escrow Deposited Recorded Earnout Payable Total Recorded Purchase Price Maximum Potential Earnout Payable (000s) Capsicum Reinsurance Brokers LLP (CRB) January 1, 2020 584 $ 62.9 $ 64.5 $ - $ - $ 129.9 $ 257.3 $ 209.1 Hanover Excess & Surplus, Inc. and Hanover Premium Finance, Inc. (HES) January 1, 2020 - - 30.1 - 3.0 - 33.1 9.3 CRES Insurance Services, LLC (CRES) June 1, 2020 288 28.5 1.5 - 1.0 5.5 36.5 7.3 Optimum Talent Inc. (OTI) November 1, 2020 102 11.1 14.1 - 3.4 14.0 42.6 21.1 Cool Insuring Agency, Inc. (CIA) December 1, 2020 406 48.4 65.0 - 7.2 8.5 129.1 30.0 Harden & Associates, Inc. (HAI) December 1, 2020 49 - 95.6 - 6.2 10.0 111.8 22.5 Ashton Tiffany, LLC (AT) December 31, 2020 - - 48.3 48.2 - 9.0 105.5 20.0 Twenty other acquisitions completed in 2020 414 38.8 79.2 1.8 9.9 30.5 160.2 68.6 1,843 $ 189.7 $ 398.3 $ 50.0 $ 30.7 $ 207.4 $ 876.1 $ 387.9
Summary of Estimated Fair Values of Net Assets Acquired	The following is a summary of the estimated fair values of the net assets acquired at the date of each acquisition made in 2020 (in millions): CRB HES CRES OTI CIA HAI AT Twenty Other Acquisitions Total Cash and restricted cash $ - $ 3.3 $ 4.3 $ 0.6 $ 4.2 $ 2.3 $ 6.0 $ 13.3 $ 34.0 Other current assets - 1.0 12.4 3.0 28.8 9.0 8.6 25.2 88.0 Fixed assets - - - 0.9 0.1 1.1 0.5 0.6 3.2 Noncurrent assets 7.6 0.8 - 6.7 0.9 6.4 2.1 3.1 27.6 Goodwill 108.4 19.1 21.3 25.4 58.9 45.7 14.8 66.0 359.6 Expiration lists 133.7 13.7 13.9 18.3 56.2 62.5 78.2 90.7 467.2 Non-compete agreements 2.9 0.1 - 0.4 0.8 0.7 5.8 0.7 11.4 Trade names 4.7 - 0.3 - 7.5 - - - 12.5 Total assets acquired 257.3 38.0 52.2 55.3 157.4 127.7 116.0 199.6 1,003.5 Current liabilities - 4.4 15.7 5.2 28.1 9.5 8.4 32.3 103.6 Noncurrent liabilities - 0.5 - 7.5 0.2 6.4 2.1 7.1 23.8 Total liabilities assumed - 4.9 15.7 12.7 28.3 15.9 10.5 39.4 127.4 Total net assets acquired $ 257.3 $ 33.1 $ 36.5 $ 42.6 $ 129.1 $ 111.8 $ 105.5 $ 160.2 $ 876.1
Summary of Unaudited Pro Forma Historical Results	The following is a summary of the unaudited pro forma historical results, as if these entities had been acquired at January 1, 2019 (in millions, except per share data): Year Ended December 31, 2020 2019 Total revenues $ 7,108.7 $ 7,352.7 Net earnings attributable to controlling interests 817.6 670.5 Basic net earnings per share 4.26 3.57 Diluted net earnings per share 4.17 3.49

Contracts with Customers (Table

Contracts with Customers (Tables)	12 Months Ended
Contracts with Customers (Tables)	Dec. 31, 2020
Revenue From Contract With Customer [Abstract]
Summary of Unbilled Receivables, Contract Assets and Contract Liabilities from Contracts with Customers	Information about unbilled receivables, contract assets and contract liabilities from contracts with customers is as follows (in millions): December 31, 2020 December 31, 2019 Unbilled receivables $ 603.1 $ 556.4 Deferred contract costs 102.0 98.3 Deferred revenue 541.3 503.8
Summary of Changes in Deferred Revenue Balances	Significant changes in the deferred revenue balances, which include foreign currency translation adjustments, during the period are as follows (in millions): Brokerage Risk Management Total Deferred revenue at December 31, 2018 $ 284.7 $ 173.0 $ 457.7 Incremental deferred revenue 254.7 109.6 364.3 Revenue recognized during the year ended December 31, 2019 included in deferred revenue at December 31, 2018 (227.5 ) (122.0 ) (349.5 ) Net change in collected billings/deposits received from customers (6.7 ) 5.6 (1.1 ) Impact of changes in foreign exchange rates 1.4 0.4 1.8 Deferred revenue recognized from business acquisitions 30.6 — 30.6 Deferred revenue at December 31, 2019 337.2 166.6 503.8 Incremental deferred revenue 282.7 91.3 374.0 Revenue recognized during the year ended December 31, 2020 included in deferred revenue at December 31, 2019 (283.1 ) (99.2 ) (382.3 ) Net change in collected billings/deposits received from customers (0.7 ) 26.3 25.6 Impact of changes in foreign exchange rates 8.7 1.6 10.3 Deferred revenue recognized from business acquisitions 9.9 — 9.9 Deferred revenue at December 31, 2020 $ 354.7 $ 186.6 $ 541.3
Summary of Expected Revenue Related to Performance Obligations	The estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied (or partially unsatisfied) at the end of the reporting period is as follows (in millions): Brokerage Risk Management Total 2021 $ 328.4 $ 122.8 $ 451.2 2022 23.6 31.2 54.8 2023 1.4 14.2 15.6 2024 0.6 6.5 7.1 2025 0.4 4.0 4.4 Thereafter 0.3 7.9 8.2 Total $ 354.7 $ 186.6 $ 541.3

Other Financial Data (Tables)

Other Financial Data (Tables)	12 Months Ended
Other Financial Data (Tables)	Dec. 31, 2020
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Summary of Major Classes of Other Current Assets	Major classes of other current assets consist of the following (in millions): December 31, 2020 2019 Premium finance advances and loans $ 442.7 $ 388.1 Accrued supplemental, direct bill and other receivables 361.7 369.1 Refined coal production related receivables 95.4 103.4 Deferred contract costs 102.0 98.3 Prepaid expenses 112.1 115.5 Total other current assets $ 1,113.9 $ 1,074.4

Fixed Assets (Tables)

Fixed Assets (Tables)	12 Months Ended
Fixed Assets (Tables)	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Summary of Fixed Assets	Major classes of fixed assets consist of the following (in millions): December 31, 2020 2019 Office equipment $ 33.0 $ 32.6 Furniture and fixtures 138.3 126.0 Leasehold improvements 166.0 150.2 Computer equipment 214.2 176.3 Land and buildings - corporate headquarters 145.1 144.9 Software 452.2 392.3 Other 16.7 19.0 Work in process 14.1 18.0 1,179.6 1,059.3 Accumulated depreciation (728.9 ) (591.9 ) Net fixed assets $ 450.7 $ 467.4

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
Intangible Assets (Tables)	Dec. 31, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Carrying Amount of Goodwill Allocated by Domestic and Foreign Operations	The carrying amount of goodwill at December 31, 2020 and 2019 allocated by domestic and foreign operations is as follows (in millions): Brokerage Risk Management Corporate Total At December 31, 2020 United States $ 3,399.8 $ 33.2 $ - $ 3,433.0 United Kingdom 1,328.3 15.1 - 1,343.4 Canada 492.9 - - 492.9 Australia 462.1 11.5 - 473.6 New Zealand 221.9 10.7 - 232.6 Other foreign 148.6 - 2.9 151.5 Total goodwill - net $ 6,053.6 $ 70.5 $ 2.9 $ 6,127.0 At December 31, 2019 United States 3,163.8 33.1 - 3,196.9 United Kingdom 1,177.8 12.9 - 1,190.7 Canada 454.4 - - 454.4 Australia 416.5 10.5 - 427.0 New Zealand 208.0 10.1 - 218.1 Other foreign 128.4 - 3.0 131.4 Total goodwill - net $ 5,548.9 $ 66.6 $ 3.0 $ 5,618.5
Changes in Carrying Amount of Goodwill	The changes in the carrying amount of goodwill for 2020 and 2019 are as follows (in millions): Brokerage Risk Management Corporate Total Balance as of December 31, 2018 $ 4,573.6 $ 49.3 $ 2.7 $ 4,625.6 Goodwill acquired during the year 958.4 16.9 0.4 975.7 Goodwill adjustments related to appraisals and other acquisition adjustments 0.2 (0.2 ) - - Goodwill written-off related to sales of business (7.2 ) - - (7.2 ) Foreign currency translation adjustments during the year 23.9 0.6 (0.1 ) 24.4 Balance as of December 31, 2019 5,548.9 66.6 3.0 5,618.5 Goodwill acquired during the year 359.6 - - 359.6 Goodwill adjustments related to appraisals and other acquisition adjustments 29.8 1.7 - 31.5 Foreign currency translation adjustments during the year 115.3 2.2 (0.1 ) 117.4 Balance as of December 31, 2020 $ 6,053.6 $ 70.5 $ 2.9 $ 6,127.0
Major Classes of Amortizable Intangible Assets	Major classes of amortizable intangible assets consist of the following (in millions): December 31, 2020 2019 Expiration lists $ 4,753.2 $ 4,246.0 Accumulated amortization - expiration lists (2,436.7 ) (2,004.3 ) 2,316.5 2,241.7 Non-compete agreements 75.9 68.4 Accumulated amortization - non-compete agreements (57.8 ) (52.5 ) 18.1 15.9 Trade names 107.8 91.8 Accumulated amortization - trade names (42.5 ) (30.7 ) 65.3 61.1 Net amortizable assets $ 2,399.9 $ 2,318.7
Estimated Aggregate Amortization Expense	Estimated aggregate amortization expense for each of the next five years is as follows (in millions): 2021 $ 378.4 2022 352.3 2023 327.1 2024 291.3 2025 251.3 Thereafter 799.5 Total $ 2,399.9

Credit and Other Debt Agreeme_2

Credit and Other Debt Agreements (Tables)	12 Months Ended
Credit and Other Debt Agreements (Tables)	Dec. 31, 2020
Debt Disclosure [Abstract]
Summary of Corporate and Other Debt	The following is a summary of our corporate and other debt (in millions): December 31, 2020 2019 Note Purchase Agreements: Semi-annual payments of interest, fixed rate of 3.48%, balloon due June 24, 2020 $ - $ 50.0 Semi-annual payments of interest, fixed rate of 3.99%, balloon due July 10, 2020 - 50.0 Semi-annual payments of interest, fixed rate of 5.18%, balloon due February 10, 2021 75.0 75.0 Semi-annual payments of interest, fixed rate of 3.69%, balloon due June 14, 2022 200.0 200.0 Semi-annual payments of interest, fixed rate of 5.49%, balloon due February 10, 2023 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.13%, balloon due June 24, 2023 200.0 200.0 Quarterly payments of interest, floating rate of 90 day LIBOR plus 1.65%, balloon due August 2, 2023 (prepaid on November 3, 2020) - 50.0 Semi-annual payments of interest, fixed rate of 4.72%, balloon due February 13, 2024 100.0 100.0 Semi-annual payments of interest, fixed rate of 4.58%, balloon due February 27, 2024 325.0 325.0 Quarterly payments of interest, floating rate of 90 day LIBOR plus 1.40%, balloon due June 13, 2024 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.31%, balloon due June 24, 2025 200.0 200.0 Semi-annual payments of interest, fixed rate of 4.85%, balloon due February 13, 2026 140.0 140.0 Semi-annual payments of interest, fixed rate of 4.73%, balloon due February 27, 2026 175.0 175.0 Semi-annual payments of interest, fixed rate of 4.40%, balloon due June 2, 2026 175.0 175.0 Semi-annual payments of interest, fixed rate of 4.36%, balloon due June 24, 2026 150.0 150.0 Semi-annual payments of interest, fixed rate of 3.75%, balloon due January 30, 2027 30.0 - Semi-annual payments of interest, fixed rate of 4.09%, balloon due June 27, 2027 125.0 125.0 Semi-annual payments of interest, fixed rate of 4.09%, balloon due August 2, 2027 125.0 125.0 Semi-annual payments of interest, fixed rate of 4.14%, balloon due August 4, 2027 98.0 98.0 Semi-annual payments of interest, fixed rate of 3.46%, balloon due December 1, 2027 100.0 100.0 Semi-annual payments of interest, fixed rate of 4.55%, balloon due June 2, 2028 75.0 75.0 Semi-annual payments of interest, fixed rate of 4.34%, balloon due June 13, 2028 125.0 125.0 Semi-annual payments of interest, fixed rate of 5.04%, balloon due February 13, 2029 100.0 100.0 Semi-annual payments of interest, fixed rate of 4.98%, balloon due February 27, 2029 100.0 100.0 Semi-annual payments of interest, fixed rate of 4.19%, balloon due June 27, 2029 50.0 50.0 Semi-annual payments of interest, fixed rate of 4.19%, balloon due August 2, 2029 50.0 50.0 Semi-annual payments of interest, fixed rate of 3.48%, balloon due December 2, 2029 50.0 50.0 Semi-annual payments of interest, fixed rate of 3.99%, balloon due January 30, 2030 341.0 - Semi-annual payments of interest, fixed rate of 4.44%, balloon due June 13, 2030 125.0 125.0 Semi-annual payments of interest, fixed rate of 5.14%, balloon due March 13, 2031 180.0 180.0 Semi-annual payments of interest, fixed rate of 4.70%, balloon due June 2, 2031 25.0 25.0 Semi-annual payments of interest, fixed rate of 4.09%, balloon due January 30, 2032 69.0 - Semi-annual payments of interest, fixed rate of 4.34%, balloon due June 27, 2032 75.0 75.0 Semi-annual payments of interest, fixed rate of 4.34%, balloon due August 2, 2032 75.0 75.0 Semi-annual payments of interest, fixed rate of 4.59%, balloon due June 13, 2033 125.0 125.0 Semi-annual payments of interest, fixed rate of 5.29%, balloon due March 13, 2034 40.0 40.0 Semi-annual payments of interest, fixed rate of 4.48%, balloon due June 12, 2034 175.0 175.0 Semi-annual payments of interest, fixed rate of 4.24%, balloon due January 30, 2035 79.0 - Semi-annual payments of interest, fixed rate of 4.69%, balloon due June 13, 2038 75.0 75.0 Semi-annual payments of interest, fixed rate of 5.45%, balloon due March 13, 2039 40.0 40.0 Semi-annual payments of interest, fixed rate of 4.49%, balloon due January 30, 2040 56.0 - Total Note Purchase Agreements 4,348.0 3,923.0 Credit Agreement: Periodic payments of interest and principal, prime or LIBOR plus up to 1.45%, expires June 7, 2024 - 520.0 Premium Financing Debt Facility - expires September 15, 2022: Facility B AUD denominated tranche, interbank rates plus 1.400% 193.1 142.1 NZD denominated tranche, interbank rates plus 1.750% - - Facility C and D AUD denominated tranche, interbank rates plus 0.730% - 18.8 NZD denominated tranche, interbank rates plus 0.940% 10.5 9.7 Total Premium Financing Debt Facility 203.6 170.6 Total corporate and other debt 4,551.6 4,613.6 Less unamortized debt acquisition costs on Note Purchase Agreements (7.0 ) (6.9 ) Net corporate and other debt $ 4,544.6 $ 4,606.7

Earnings per Share (Tables)

Earnings per Share (Tables)	12 Months Ended
Earnings per Share (Tables)	Dec. 31, 2020
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net EPS	The following table sets forth the computation of basic and diluted net earnings per share (in millions, except per share data): Year Ended December 31, 2020 2019 2018 Net earnings attributable to controlling interests $ 818.8 $ 668.8 $ 633.5 Weighted average number of common shares outstanding 191.0 186.0 182.7 Dilutive effect of stock options using the treasury stock method 4.0 4.1 3.5 Weighted average number of common and common equivalent shares outstanding 195.0 190.1 186.2 Basic net earnings per share $ 4.29 $ 3.60 $ 3.47 Diluted net earnings per share $ 4.20 $ 3.52 $ 3.40

Stock Option Plans (Tables)

Stock Option Plans (Tables)	12 Months Ended
Stock Option Plans (Tables)	Dec. 31, 2020
Text Block [Abstract]
Black-Scholes Option Pricing Model with Weighted Average	For purposes of expense recognition in 2020, 2019 and 2018, the estimated fair values of the stock option grants are amortized to expense over the options’ vesting period. We estimated the fair value of stock options at the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions: Year Ended December 31, 2020 2019 2018 Expected dividend yield 2.1 % 1.7 % 2.3 % Expected risk-free interest rate 0.7 % 2.5 % 2.7 % Volatility 17.3 % 15.6 % 15.1 % Expected life (in years) 5.4 5.5 5.5
Stock Option Activity and Related Information	The following is a summary of our stock option activity and related information for 2020 and 2019 (in millions, except exercise price and year data): Weighted Average Weighted Remaining Shares Average Contractual Aggregate Under Exercise Term Intrinsic Option Price (in years) Value Year Ended December 31, 2020 Beginning balance 7.9 $ 56.40 Granted 1.6 86.17 Exercised (1.8 ) 45.80 Forfeited or canceled (0.2 ) 65.87 Ending balance 7.5 $ 65.09 3.86 $ 437.9 Exercisable at end of year 1.9 $ 47.17 1.83 $ 147.2 Ending unvested and expected to vest 5.3 $ 70.74 4.51 $ 278.1 Year Ended December 31, 2019 Beginning balance 8.8 $ 50.16 Granted 1.3 79.59 Exercised (1.9 ) 42.91 Forfeited or canceled (0.3 ) 57.33 Ending balance 7.9 $ 56.40 3.75 $ 308.6 Exercisable at end of year 2.0 $ 45.03 1.82 $ 101.9 Ending unvested and expected to vest 5.7 $ 59.76 4.36 $ 201.5
Other Information Regarding Stock Options Outstanding and Exercisable	Other information regarding stock options outstanding and exercisable at December 31, 2020 is summarized as follows (in millions, except exercise price and year data): Options Outstanding Options Exercisable Weighted Average Remaining Weighted Weighted Contractual Average Average Number Term Exercise Number Exercise Range of Exercise Prices Outstanding (in years) Price Exercisable Price $ 43.71 — $ 43.71 1.4 2.21 $ 43.71 0.7 $ 43.71 46.17 — 46.87 0.9 0.97 46.33 0.9 46.33 49.55 — 56.86 1.3 3.21 56.83 0.3 56.81 70.74 — 70.74 1.1 4.21 70.74 — 70.74 79.59 — 79.59 1.2 5.20 79.59 — 79.59 86.17 — 86.17 1.6 6.20 86.17 — — $ 43.71 — $ 86.17 7.5 3.86 $ 65.09 1.9 $ 47.17

Restricted Stock, Performance_2

Restricted Stock, Performance Share and Cash Awards (Tables)	12 Months Ended
	Dec. 31, 2020
Text Block [Abstract]
Schedule of Restricted Stock Awards Vesting Periods	The vesting periods of the 2020, 2019 and 2018 restricted stock unit awards are as follows (in actual shares): Restricted Stock Units Granted Vesting Period 2020 2019 2018 One year 16,740 14,800 18,900 Two years 8,870 12,000 12,700 Five years 397,000 387,900 407,500 Total shares granted 422,610 414,700 439,100

Retirement Plans (Tables)

Retirement Plans (Tables)	12 Months Ended
Retirement Plans (Tables)	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Reconciliation of Balances of Pension Benefit Obligation and Fair Value of Plan Assets	A reconciliation of the beginning and ending balances of the pension benefit obligation and fair value of plan assets and the funded status of the plan is as follows (in millions): Year Ended December 31, 2020 2019 Change in pension benefit obligation: Benefit obligation at beginning of year $ 274.4 $ 253.2 Service cost 0.8 1.6 Interest cost 8.0 9.8 Net actuarial loss 22.6 24.7 Benefits paid (15.2 ) (14.9 ) Benefit obligation at end of year $ 290.6 $ 274.4 Change in plan assets: Fair value of plan assets at beginning of year $ 243.7 $ 220.0 Actual return on plan assets 34.3 38.6 Contributions by the company — — Benefits paid (15.2 ) (14.9 ) Fair value of plan assets at end of year $ 262.8 $ 243.7 Funded status of the plan (underfunded) $ (27.8 ) $ (30.7 ) Amounts recognized in the consolidated balance sheet consist of: Noncurrent liabilities - accrued benefit liability $ (27.8 ) $ (30.7 ) Accumulated other comprehensive loss - net actuarial loss 68.3 69.8 Net amount included in retained earnings $ 40.5 $ 39.1
Components of Net Periodic Pension Benefit Cost and Other Changes in Plan Assets and Obligations Recognized in Earnings and Other Comprehensive Earnings	The components of the net periodic pension benefit cost for the plan and other changes in plan assets and obligations recognized in earnings and other comprehensive earnings consist of the following (in millions): Year Ended December 31, 2020 2019 2018 Net periodic pension cost: Service cost $ 0.8 $ 1.6 $ 0.8 Interest cost on benefit obligation 8.0 9.8 9.3 Expected return on plan assets (16.4 ) (14.8 ) (16.0 ) Amortization of net loss 6.2 7.0 4.9 Net periodic benefit cost (1.4 ) 3.6 (1.0 ) Other changes in plan assets and obligations recognized in other comprehensive earnings: Net loss incurred 4.7 0.8 17.2 Amortization of net loss (6.2 ) (7.0 ) (4.9 ) Total recognized in other comprehensive loss (1.5 ) (6.2 ) 12.3 Total recognized in net periodic pension cost and other comprehensive loss $ (2.9 ) $ (2.6 ) $ 11.3 Estimated amortization for the following year: Amortization of net loss $ 5.8 $ 6.1 $ 7.2
Weighted Average Assumptions of Pension Benefit Obligation and Net Periodic Pension Benefit Cost	The following weighted average assumptions were used at December 31 in determining the plan’s pension benefit obligation: December 31, 2020 2019 Discount rate 2.25 % 3.00 % Weighted average expected long-term rate of return on plan assets 7.00 % 7.00 % The following weighted average assumptions were used at January 1 in determining the plan’s net periodic pension benefit cost: Year Ended December 31, 2020 2019 2018 Discount rate 3.00 % 4.00 % 3.50 % Weighted average expected long-term rate of return on plan assets 7.00 % 7.00 % 7.00 %
Schedule of Benefit Payments Expected to be Paid by Plan	The following benefit payments are expected to be paid by the plan (in millions): 2021 $ 16.2 2022 16.5 2023 16.7 2024 16.7 2025 16.9 Years 2026 to 2030 83.1
Summary of Plans Weighted Average Asset Allocations	The following is a summary of the plan’s weighted average asset allocations at December 31 by asset category: December 31, Asset Category 2020 2019 Equity securities 63.0 % 61.0 % Debt securities 30.0 % 32.0 % Real estate 7.0 % 7.0 % Total 100.0 % 100.0 %
Summary of Plan's Assets Carried at Fair Value	The following is a summary of the plan’s assets carried at fair value as of December 31 by level within the fair value hierarchy (in millions): December 31, Fair Value Hierarchy 2020 2019 Level 1 $ — $ — Level 2 141.8 135.8 Level 3 121.0 107.9 Total fair value $ 262.8 $ 243.7
Reconciliation of Beginning and Ending Balances for Level 3 Assets of Plan Measured at Fair Value	The following is a reconciliation of the beginning and ending balances for the Level 3 assets of the plan measured at fair value (in millions): Year Ended December 31, 2020 2019 Fair value at January 1 $ 107.9 $ 94.9 Settlements (2.7 ) — Unrealized gain 15.8 13.0 Fair value at December 31 $ 121.0 $ 107.9

Investments (Tables)

Investments (Tables)	12 Months Ended
Investments (Tables)	Dec. 31, 2020
Equity Method Investments And Joint Ventures [Abstract]
Investments Reported in Other Current and Non-Current Assets	The following is a summary of our investments included in other noncurrent assets in the consolidated balance sheet (in millions): December 31, 2020 2019 Assets Funding commitments Assets Chem-Mod LLC $ 4.0 $ - $ 4.0 Chem-Mod International LLC 2.0 - 2.0 Clean-coal investments: Controlling interest in limited liability companies that own fourteen 2009 Era Clean Coal Plants - - - Non-controlling interest in a limited liability company that owns one 2011 Era Clean Coal Plant 0.1 - 0.3 Controlling interest in limited liability companies that own twenty 2011 Era Clean Coal Plants 12.4 0.9 29.2 Other investments 3.9 4.5 Total investments $ 22.4 $ 0.9 $ 40.0

Leases (Tables)

Leases (Tables)	12 Months Ended
Leases (Tables)	Dec. 31, 2020
Leases [Abstract]
Components of Lease Expense	The components of lease expense are as follows (in millions): Statement of Earnings Year ended Lease Components Classification December 31, 2020 Operating lease expense Operating expense $ 126.5 Variable lease expense Operating expense 22.0 Sublease income Investment income (1.1 ) Total net lease expense $ 147.4
Summary of Supplemental Cash Flow Information Related to Leases	Year ended Supplemental Cash Flow Information Related to Leases (in millions) December 31, 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 120.1 Right-of-use assets obtained in exchange for new operating lease liabilities $ 71.2
Summary of Supplemental Balance Sheet Information Related to Leases	Supplemental balance sheet information related to leases is as follows (in millions, except lease term and discount rate): Lease Components Balance Sheet Classification December 31, 2020 Lease right-of-use assets Right-of-use assets $ 373.9 Other current lease liabilities Accrued compensation and other current liabilities 88.8 Lease liabilities Lease liabilities - noncurrent 320.9 Total lease liabilities $ 409.7 Weighted-average remaining lease term, years 5.3 Weighted-average discount rate 3.6 %
Maturities of Operating Lease Liabilities	Maturities of operating lease liabilities for each of the next five years and thereafter are as follows (in millions): 2021 $ 108.5 2022 93.9 2023 75.1 2024 54.8 2025 41.6 Thereafter 77.8 Total lease payments 451.7 Less interest (42.0 ) Total $ 409.7

Derivatives and Hedging Activ_2

Derivatives and Hedging Activity (Tables)	12 Months Ended
Derivatives and Hedging Activity (Tables)	Dec. 31, 2020
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Summary of Notional and Fair Values of Derivative Instruments	The notional and fair values of derivatives designated as hedging instruments are as follows at December 31, 2020 and 2019 (in millions): Derivative Assets Derivative Liabilities Notional Balance Sheet Fair Balance Sheet Fair Instrument Amount Classification Value Classification Value At December 31, 2020 Interest rate contracts $ 550.0 Other current assets $ — Accrued compensation and $ 54.5 Other noncurrent assets — other current liabilities Other noncurrent liabilities 10.9 Foreign exchange contracts (1) 48.6 Other current assets 5.9 Accrued compensation and 0.6 other current liabilities Other noncurrent assets 7.8 Other noncurrent liabilities 3.3 Total $ 598.6 $ 13.7 $ 69.3 At December 31, 2019 Interest rate contracts $ 800.0 Other current assets $ 2.8 Accrued compensation and $ 25.0 Other noncurrent assets 5.4 other current liabilities Other noncurrent liabilities 23.0 Foreign exchange contracts (1) 31.7 Other current assets 4.5 Accrued compensation and 1.8 other current liabilities Other noncurrent assets 8.5 Other noncurrent liabilities 2.6 Total $ 831.7 $ 21.2 $ 52.4 ( 1) Included within foreign exchange contracts at December 31, 2020 were $354.7 million of call options offset with $354.7 million of put options, and $9.0 million of buy forwards offset with $57.6 million of sell forwards.
Summary of Amounts of Derivative Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	The effect of cash flow hedge accounting on accumulated other comprehensive loss were as follows (in millions): Instrument Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss (1) Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Earnings Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing Statement of Earnings Classification Year ended December 31, 2020 Interest rate contracts $ (92.5 ) $ (1.1 ) $ — Interest expense Foreign exchange contracts (4.6 ) (2.4 ) (0.4 ) Commission revenue (1.6 ) 1.6 Compensation expense (1.2 ) 1.1 Operating expense Total $ (97.1 ) $ (6.3 ) $ 2.3 Year ended December 31, 2019 Interest rate contracts $ (47.0 ) $ (1.2 ) $ — Interest expense Foreign exchange contracts 9.9 (1.6 ) (0.8 ) Commission revenue (1.4 ) 1.2 Compensation expense (1.0 ) 0.9 Operating expense Total $ (37.1 ) $ (5.2 ) $ 1.3 (1) During 2020, the amount excluded from the assessment of hedge effectiveness for our foreign exchange contracts recognized in accumulated other comprehensive loss was a loss of $1.3 million.

Commitments, Contingencies an_2

Commitments, Contingencies and Off-Balance Sheet Arrangements (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Contractual Obligations	Our future minimum cash payments, including interest, associated with our contractual obligations pursuant to the note purchase agreements, Credit Agreement, Premium Financing Debt Facility, operating leases and purchase commitments at December 31, 2020 were as follows (in millions): Payments Due by Period Contractual Obligations 2021 2022 2023 2024 2025 Thereafter Total Note purchase agreements $ 75.0 $ 200.0 $ 250.0 $ 475.0 $ 200.0 $ 3,148.0 $ 4,348.0 Credit Agreement — — — — — — — Premium Financing Debt Facility 203.6 — — — — — 203.6 Interest on debt 189.5 183.6 174.7 158.0 143.4 601.9 1,451.1 Total debt obligations 468.1 383.6 424.7 633.0 343.4 3,749.9 6,002.7 Operating lease obligations 108.5 93.9 75.1 54.8 41.6 77.8 451.7 Less sublease arrangements (0.3 ) (0.3 ) (0.2 ) (0.2 ) (0.2 ) (0.5 ) (1.7 ) Outstanding purchase obligations 75.3 49.4 30.8 21.9 16.7 22.7 216.8 Total contractual obligations $ 651.6 $ 526.6 $ 530.4 $ 709.5 $ 401.5 $ 3,849.9 $ 6,669.5
Off-Balance Sheet Commitments	Off-Balance Sheet Commitments Our total unrecorded commitments associated with outstanding letters of credit, financial guarantees and funding commitments at December 31, 2020 were as follows (in millions): Amount of Commitment Expiration by Period Off-Balance Sheet Commitments 2021 2022 2023 2024 2025 Thereafter Total Amounts Committed Letters of credit $ — $ — $ — $ — $ — $ 18.4 $ 18.4 Financial guarantees 0.2 0.2 0.2 0.2 0.2 0.2 1.2 Total commitments $ 0.2 $ 0.2 $ 0.2 $ 0.2 $ 0.2 $ 18.6 $ 19.6
Outstanding Letters of Credit and Funding Commitments	Our commitments associated with outstanding letters of credit, financial guarantees and funding commitments at December 31, 2020 were as follows (all dollar amounts in table are in millions): Description, Purpose and Trigger Collateral Compensation to Us Maximum Exposure Liability Recorded Credit support under letters of credit (LOC) for deductibles due by us on our own insurance coverages - expires after 2025 None None $ 9.4 $ 17.5 Trigger - We do not reimburse the insurance companies for deductibles the insurance companies advance on our behalf Credit enhancement under letters of credit for our captive insurance operations to meet minimum statutory capital requirements - expires after 2025 None Reimbursement of LOC fees 7.5 - Trigger - Dissolution or catastrophic financial results of the operation Collateral related to claims funds held in a fiduciary capacity by a recent acquisition - expires 2021 None None 1.0 - Trigger - Claim payments are not made Credit support under letters of credit in lieu of a security deposit for an acquisition's lease - expires after 2025 None None 0.5 - Trigger - Lease payments do not get made Financial guarantees of loans to 5 Canadian-based employees - expires when loan balances are reduced to zero through May 2029 - Principal and interest payments are paid quarterly (1) None 1.2 - Trigger - Default on loan payments $ 19.6 $ 17.5

Insurance Operations (Tables)

Insurance Operations (Tables)	12 Months Ended
Insurance Operations (Tables)	Dec. 31, 2020
Insurance [Abstract]
Summary of Reconciliations of Direct to Net premiums on Written and Earned Basis Related to Wholly Owned Underwriting Enterprise Subsidiary	Reconciliations of direct to net premiums, on a written and earned basis, for 2020, 2019 and 2018 related to the wholly-owned underwriting enterprise subsidiary 2020 2019 2018 Written Earned Written Earned Written Earned Direct $ 37.7 $ 40.7 $ 44.6 $ 59.1 $ 57.6 $ 53.2 Assumed 0.1 0.9 1.0 1.9 4.7 4.6 Ceded (37.8 ) (41.6 ) (45.6 ) (61.0 ) (62.3 ) (57.8 ) Net $ - $ - $ - $ - $ - $ -

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Components of Earnings Before Income Taxes and Provision for Income Taxes	Significant components of earnings before income taxes and the provision for income taxes are as follows (in millions): Year Ended December 31, 2020 2019 2018 Earnings before income taxes: United States $ 524.4 $ 388.4 $ 337.6 Foreign, principally Australia, Canada, New Zealand and the U.K. 346.5 237.7 141.8 Total earnings before income taxes $ 870.9 $ 626.1 $ 479.4 Provision (benefit) for income taxes: Federal: Current $ 43.6 $ 3.8 $ — Deferred (112.4 ) (142.5 ) (214.0 ) (68.8 ) (138.7 ) (214.0 ) State and local: Current 36.6 11.1 15.4 Deferred (19.3 ) (6.0 ) (29.0 ) 17.3 5.1 (13.6 ) Foreign: Current 94.6 66.6 60.7 Deferred (30.3 ) (22.7 ) (29.6 ) 64.3 43.9 31.1 Total provision (benefit) for income taxes $ 12.8 $ (89.7 ) $ (196.5 )
Reconciliation of Provision for Income Taxes with Federal Statutory Income Tax Rate	A reconciliation of the provision for income taxes with the U.S. federal statutory income tax rate is as follows (in millions, except percentages): Year Ended December 31, 2020 2019 2018 Amount % of Pretax Earnings Amount % of Pretax Earnings Amount % of Pretax Earnings Federal statutory rate $ 182.9 21.0 $ 131.5 21.0 $ 100.7 21.0 State income taxes - net of Federal benefit 22.2 2.6 4.4 0.7 8.5 1.8 Differences related to non U.S. operations (2.5 ) (0.3 ) (10.1 ) (1.6 ) (14.8 ) (3.1 ) Alternative energy and other tax credits (154.3 ) (17.7 ) (196.1 ) (31.3 ) (252.9 ) (52.8 ) Other permanent differences (15.7 ) (1.8 ) (7.6 ) (1.2 ) 0.9 0.2 U.S. repatriation tax - - - - (1.8 ) (0.4 ) Stock-based compensation (31.4 ) (3.6 ) (16.2 ) (2.6 ) (15.0 ) (3.1 ) Changes in unrecognized tax benefits - - 0.8 0.1 (0.2 ) - Change in valuation allowance 6.5 0.7 7.5 1.2 (22.0 ) (4.6 ) Change in tax rates 5.5 0.6 (3.7 ) (0.6 ) - - Other (0.4 ) - (0.2 ) - 0.1 - Provision (benefit) for income taxes $ 12.8 $ 1.5 $ (89.7 ) $ (14.3 ) $ (196.5 ) $ (41.0 )
Gross Unrecognized Tax Benefits	A reconciliation of the beginning and ending balances of the total amounts of gross unrecognized tax benefits is as follows (in millions): December 31, 2020 2019 Gross unrecognized tax benefits at January 1 $ 11.5 $ 10.7 Increases in tax positions for current year 2.9 2.1 Settlements (1.1 ) (0.4 ) Lapse in statute of limitations (1.2 ) (1.1 ) Increases in tax positions for prior years 0.2 0.6 Decreases in tax positions for prior years (1.1 ) (0.4 ) Gross unrecognized tax benefits at December 31 $ 11.2 $ 11.5
Deferred Tax Assets and Liabilities	Significant components of our deferred tax assets and liabilities are as follows (in millions): December 31, 2020 2019 Deferred tax assets: Alternative minimum tax and other credit carryforwards $ 998.0 $ 962.1 Accrued and unfunded compensation and employee benefits 239.9 156.0 Amortizable intangible assets 61.3 54.3 Compensation expense related to stock options 14.4 11.3 Accrued liabilities 65.7 63.9 Accrued pension liability 9.3 9.9 Investments 1.3 0.9 Net operating loss carryforwards 36.1 37.2 Capital loss carryforwards 9.0 12.6 Lease liabilities 96.3 65.3 Hedging instruments 34.6 11.7 Other 2.8 4.3 Total deferred tax assets 1,568.7 1,389.5 Valuation allowance for deferred tax assets (94.9 ) (80.5 ) Deferred tax assets 1,473.8 1,309.0 Deferred tax liabilities: Nondeductible amortizable intangible assets 316.9 322.4 Investment-related partnerships 8.5 9.1 Depreciable fixed assets 32.4 22.4 Right-of-use assets 92.2 62.6 Revenue recognition 33.1 63.7 Other prepaid items 12.0 10.6 Total deferred tax liabilities 495.1 490.8 Net deferred tax assets $ 978.7 $ 818.2

Supplemental Disclosures of C_2

Supplemental Disclosures of Cash Flow Information (Tables)	12 Months Ended
Supplemental Disclosures of Cash Flow Information (Tables)	Dec. 31, 2020
Cash And Cash Equivalents [Abstract]
Supplemental disclosures of cash flow information	Year ended December 31, Supplemental disclosures of cash flow information (in millions): 2020 2019 2018 Interest paid $ 188.9 $ 169.2 $ 139.2 Income taxes paid, net 113.0 22.2 68.1
Summary of Cash, Cash Equivalents and Restricted Cash	The following is a reconciliation of our end of period cash, cash equivalents and restricted cash balances as presented in the consolidated statement of cash flows for the years ended December 31, 2020, 2019 and 2018 (in millions): December 31, 2020 2019 2018 Cash and cash equivalents $ 664.6 $ 604.8 $ 607.2 Restricted cash 2,909.7 2,019.1 1,629.6 Total cash, cash equivalents and restricted cash $ 3,574.3 $ 2,623.9 $ 2,236.8

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Earnings (Tables)	12 Months Ended
Accumulated Other Comprehensive Earnings (Tables)	Dec. 31, 2020
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Earnings (Loss) Attributable to Controlling Interests	The after-tax components of our accumulated comprehensive earnings (loss) attributable to controlling interests consist of the following (in millions): Pension Liability Foreign Currency Translation Fair Value of Derivative Instruments Accumulated Comprehensive Earnings (Loss) Balance as of January 1, 2018 $ (43.0 ) $ (521.3 ) $ 8.9 $ (555.4 ) Reclassification to retained earnings of income tax effects related to the TCJA (7.9 ) — 1.3 (6.6 ) Net change in period (10.3 ) (197.7 ) (15.6 ) (223.6 ) Balance as of December 31, 2018 (61.2 ) (719.0 ) (5.4 ) (785.6 ) Cumulative effect of adoption of new accounting standards — — (0.2 ) (0.2 ) Net change in period 4.7 44.2 (22.7 ) 26.2 Balance as of December 31, 2019 (56.5 ) (674.8 ) (28.3 ) (759.6 ) Net change in period 0.4 183.7 (68.1 ) 116.0 Balance as of December 31, 2020 $ (56.1 ) $ (491.1 ) $ (96.4 ) $ (643.6 )

Quarterly Operating Results (_2

Quarterly Operating Results (unaudited) (Tables)	12 Months Ended
Quarterly Operating Results (unaudited) (Tables)	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Operating Results	Quarterly operating results for 2020 and 2019 were as follows (in millions, except per share data): 1st 2nd 3rd 4th 2020 Total revenues $ 1,866.9 $ 1,584.0 $ 1,849.1 $ 1,703.6 Total expenses 1,510.9 1,412.3 1,639.6 1,569.9 Earnings before income taxes $ 356.0 $ 171.7 $ 209.5 $ 133.7 Net earnings attributable to controlling interests $ 346.3 $ 153.7 $ 176.6 $ 142.2 Basic net earnings per share $ 1.83 $ 0.81 $ 0.92 $ 0.74 Diluted net earnings per share $ 1.79 $ 0.79 $ 0.90 $ 0.72 2019 Total revenues $ 1,990.6 $ 1,657.8 $ 1,825.2 $ 1,721.4 Total expenses 1,668.8 1,552.3 1,710.4 1,637.4 Earnings before income taxes $ 321.8 $ 105.5 $ 114.8 $ 84.0 Net earnings attributable to controlling interests $ 334.1 $ 110.1 $ 126.1 $ 98.5 Basic net earnings per share $ 1.81 $ 0.59 $ 0.68 $ 0.53 Diluted net earnings per share $ 1.77 $ 0.58 $ 0.66 $ 0.51

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
Segment Information (Tables)	Dec. 31, 2020
Segment Reporting [Abstract]
Schedule of Segment Reporting Information by Segment	Financial information relating to our segments for 2020, 2019 and 2018 is as follows (in millions): Year Ended December 31, 2020 Brokerage Risk Management Corporate Total Revenues: Commissions $ 3,591.9 $ — $ — $ 3,591.9 Fees 1,136.9 821.0 — 1,957.9 Supplemental revenues 221.9 — — 221.9 Contingent revenues 147.0 — — 147.0 Investment income 75.2 0.7 — 75.9 Net losses on divestitures (5.8 ) — — (5.8 ) Revenue from clean coal activities — — 863.5 863.5 Other net losses — — (0.4 ) (0.4 ) Revenues before reimbursements 5,167.1 821.7 863.1 6,851.9 Reimbursements — 151.7 — 151.7 Total revenues 5,167.1 973.4 863.1 7,003.6 Compensation 2,882.5 517.5 66.5 3,466.5 Operating 687.2 162.6 56.7 906.5 Reimbursements — 151.7 — 151.7 Cost of revenues from clean coal activities — — 882.1 882.1 Interest — — 196.4 196.4 Depreciation 73.5 49.4 22.2 145.1 Amortization 411.3 6.0 — 417.3 Change in estimated acquisition earnout payables (29.7 ) (3.2 ) — (32.9 ) Total expenses 4,024.8 884.0 1,223.9 6,132.7 Earnings (loss) before income taxes 1,142.3 89.4 (360.8 ) 870.9 Provision (benefit) for income taxes 276.3 22.5 (286.0 ) 12.8 Net earnings (loss) 866.0 66.9 (74.8 ) 858.1 Net earnings attributable to noncontrolling interests 4.9 — 34.4 39.3 Net earnings (loss) attributable to controlling interests $ 861.1 $ 66.9 $ (109.2 ) $ 818.8 Net foreign exchange loss $ (2.6 ) $ (0.1 ) $ (0.2 ) $ (2.9 ) Revenues: United States $ 3,369.4 $ 816.4 $ 863.1 $ 5,048.9 United Kingdom 993.7 40.7 — 1,034.4 Australia 216.1 98.4 — 314.5 Canada 243.8 5.3 — 249.1 New Zealand 141.8 12.6 — 154.4 Other foreign 202.3 — — 202.3 Total revenues $ 5,167.1 $ 973.4 $ 863.1 $ 7,003.6 At December 31, 2020 Identifiable assets: United States $ 8,897.9 $ 716.2 $ 2,172.2 $ 11,786.3 United Kingdom 6,135.1 139.2 — 6,274.3 Australia 1,373.3 89.6 — 1,462.9 Canada 1,053.6 4.8 — 1,058.4 New Zealand 766.0 24.1 — 790.1 Other foreign 959.4 — — 959.4 Total identifiable assets $ 19,185.3 $ 973.9 $ 2,172.2 $ 22,331.4 Goodwill - net $ 6,053.6 $ 70.5 $ 2.9 $ 6,127.0 Amortizable intangible assets - net 2,376.3 23.6 — 2,399.9 Year Ended December 31, 2019 Brokerage Risk Management Corporate Total Revenues: Commissions $ 3,320.6 $ — $ — $ 3,320.6 Fees 1,074.2 836.9 — 1,911.1 Supplemental revenues 210.5 — — 210.5 Contingent revenues 135.6 — — 135.6 Investment income 85.3 1.6 — 86.9 Net gains on divestitures 75.3 — — 75.3 Revenue from clean coal activities — — 1,319.3 1,319.3 Other net losses — — (2.9 ) (2.9 ) Revenues before reimbursements 4,901.5 838.5 1,316.4 7,056.4 Reimbursements — 138.6 — 138.6 Total revenues 4,901.5 977.1 1,316.4 7,195.0 Compensation 2,745.9 515.7 77.9 3,339.5 Operating 796.5 184.9 87.1 1,068.5 Reimbursements — 138.6 — 138.6 Cost of revenues from clean coal activities — — 1,352.8 1,352.8 Interest — — 179.8 179.8 Depreciation 66.6 46.2 27.6 140.4 Amortization 329.1 4.9 — 334.0 Change in estimated acquisition earnout payables 16.9 (1.6 ) — 15.3 Total expenses 3,955.0 888.7 1,725.2 6,568.9 Earnings (loss) before income taxes 946.5 88.4 (408.8 ) 626.1 Provision (benefit) for income taxes 229.2 22.2 (341.1 ) (89.7 ) Net earnings (loss) 717.3 66.2 (67.7 ) 715.8 Net earnings attributable to noncontrolling interests 17.2 — 29.8 47.0 Net earnings (loss) attributable to controlling interests $ 700.1 $ 66.2 $ (97.5 ) $ 668.8 Net foreign exchange loss $ (1.0 ) $ (0.1 ) $ (5.6 ) $ (6.7 ) Revenues: United States $ 3,234.3 $ 828.4 $ 1,316.4 $ 5,379.1 United Kingdom 921.8 41.6 — 963.4 Australia 211.3 87.3 — 298.6 Canada 221.4 4.6 — 226.0 New Zealand 145.6 15.2 — 160.8 Other foreign 167.1 — — 167.1 Total revenues $ 4,901.5 $ 977.1 $ 1,316.4 $ 7,195.0 At December 31, 2019 Identifiable assets: United States $ 8,132.3 $ 655.6 $ 1,994.8 $ 10,782.7 United Kingdom 4,964.5 126.6 — 5,091.1 Australia 1,217.9 90.0 — 1,307.9 Canada 913.6 3.1 — 916.7 New Zealand 695.9 22.8 — 718.7 Other foreign 817.7 — — 817.7 Total identifiable assets $ 16,741.9 $ 898.1 $ 1,994.8 $ 19,634.8 Goodwill - net $ 5,548.9 $ 66.6 $ 3.0 $ 5,618.5 Amortizable intangible assets - net 2,289.9 28.8 — 2,318.7 Year Ended December 31, 2018 Brokerage Risk Management Corporate Total Revenues: Commissions $ 2,920.7 $ — $ — $ 2,920.7 Fees 958.5 797.8 — 1,756.3 Supplemental revenues 189.9 — — 189.9 Contingent revenues 98.0 — — 98.0 Investment income 69.6 0.5 — 70.1 Net gains on divestitures 10.2 — — 10.2 Revenue from clean coal activities — — 1,746.3 1,746.3 Other net gains — — 0.9 0.9 Revenues before reimbursements 4,246.9 798.3 1,747.2 6,792.4 Reimbursements — 141.6 — 141.6 Total revenues 4,246.9 939.9 1,747.2 6,934.0 Compensation 2,447.1 489.7 89.5 3,026.3 Operating 673.5 174.6 55.6 903.7 Reimbursements — 141.6 — 141.6 Cost of revenues from clean coal activities — — 1,816.0 1,816.0 Interest — — 138.4 138.4 Depreciation 60.9 38.7 28.2 127.8 Amortization 286.9 4.3 — 291.2 Change in estimated acquisition earnout payables 14.3 (4.7 ) — 9.6 Total expenses 3,482.7 844.2 2,127.7 6,454.6 Earnings (loss) before income taxes 764.2 95.7 (380.5 ) 479.4 Provision (benefit) for income taxes 191.0 25.3 (412.8 ) (196.5 ) Net earnings 573.2 70.4 32.3 675.9 Net earnings attributable to noncontrolling interests 10.7 - 31.7 42.4 Net earnings attributable to controlling interests $ 562.5 $ 70.4 $ 0.6 $ 633.5 Net foreign exchange gain $ - $ - $ 2.9 $ 2.9 Revenues: United States $ 2,840.9 $ 789.7 $ 1,747.2 $ 5,377.8 United Kingdom 738.5 35.4 — 773.9 Australia 195.9 94.7 — 290.6 Canada 181.1 4.3 — 185.4 New Zealand 141.7 15.8 — 157.5 Other foreign 148.8 — — 148.8 Total revenues $ 4,246.9 $ 939.9 $ 1,747.2 $ 6,934.0 At December 31, 2018 Identifiable assets: United States $ 6,865.4 $ 571.4 $ 1,800.8 $ 9,237.6 United Kingdom 3,758.5 103.8 — 3,862.3 Australia 1,096.1 47.2 — 1,143.3 Canada 783.1 4.4 — 787.5 New Zealand 688.5 21.3 — 709.8 Other foreign 593.5 — — 593.5 Total identifiable assets $ 13,785.1 $ 748.1 $ 1,800.8 $ 16,334.0 Goodwill - net $ 4,573.6 $ 49.3 $ 2.7 $ 4,625.6 Amortizable intangible assets - net 1,753.7 19.3 — 1,773.0

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020USD ($)CountrySegmentFacilityshares	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Significant Accounting Policies [Line Items]
Number of reportable segments \| Segment	3
Number of commercial clean coal production facilities \| Facility	35
Number of countries in which the company has operations \| Country	49
Number of countries in which the company does business through a network of correspondent brokers and consultants \| Country	150
Percentage of ownership interest	50.00%
Percentage of variable ownership interest	50.00%
Description of contracts renewal period	one year or less
Percentage of commission and fee revenues on the effective date	80.00%
Percentage of commission and fee revenues in the first three months	15.00%
Percentage of commission and fee revenues after the first three months	5.00%
Allowances for estimated policy cancellations	$ 9,900,000	$ 8,300,000
Allowance for doubtful accounts	$ 10,100,000	8,700,000
Premium financing contracts, terms	premium financing contracts are structured to minimize potential bad debt expense to us. Such receivables are generally considered delinquent after seven days of the payment due date. In normal course, insurance policies are cancelled within one month of the contractual payment due date if the payment remains delinquent.
Outstanding loan receivable	$ 442,700,000	388,100,000
Write-off of amortizable intangible assets	$ 51,700,000	$ 100,000	$ 10,600,000
Employee Stock Purchase Plan [Member]
Significant Accounting Policies [Line Items]
Shares authorized \| shares	8,000,000
Percentage of employees contribution	15.00%
Purchase price of common stock, percentage	95.00%
Aggregate fair market value of shares purchased	$ 25,000
Maximum number of shares purchased by employees \| shares	2,000
Shares available for grant \| shares	6,000,000
Maximum [Member]
Significant Accounting Policies [Line Items]
Percentage of ownership interest	50.00%
Maximum [Member] \| Expiration Lists [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives of intangibles assets, years	15 years
Maximum [Member] \| Non-Compete Agreements [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives of intangibles assets, years	6 years
Maximum [Member] \| Trade Names [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives of intangibles assets, years	15 years
Minimum [Member] \| Expiration Lists [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives of intangibles assets, years	2 years
Minimum [Member] \| Non-Compete Agreements [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives of intangibles assets, years	2 years
Minimum [Member] \| Trade Names [Member]
Significant Accounting Policies [Line Items]
Estimated useful lives of intangibles assets, years	2 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Estimated Useful Life of Fixed Assets (Detail)	12 Months Ended
	Dec. 31, 2020
Office Equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	3 years
Office Equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	10 years
Furniture and Fixtures [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	3 years
Furniture and Fixtures [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	10 years
Computer Equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	3 years
Computer Equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	5 years
Building [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	15 years
Building [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	40 years
Software [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	3 years
Software [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	5 years
Refined Fuel Plants [Member]
Property, Plant and Equipment [Line Items]
Useful life, years	10 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives, years	Shorter of the lease term or useful life of the asset

Effect of New Accounting Pron_2

Effect of New Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Right-of-use assets	$ 373.9	$ 393.5	$ 379.6
Operating lease liabilities	409.7		420.3
Net rent related asset and liabilities			38.3
Retained earnings	$ 2,371.7	$ 1,901.3
ASU 2016-02 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2019
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	false
ASU 2016-13 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU 2018-13 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU 2018-14 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU 2017-12 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2019
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	false
ASU 2017-04 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU 2018-15 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
Cumulative Effect Period Of Adoption Adjustment [Member] \| ASU 2016-02 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Retained earnings			(2.4)
Cumulative Effect Period Of Adoption Adjustment [Member] \| ASU 2017-12 [Member] \| Accumulated Other Comprehensive Loss [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Retained earnings			$ 0.2

Business Combinations - Acquisi

Business Combinations - Acquisition Method for Recording Business Combinations (Detail) shares in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)shares
Business Acquisition [Line Items]
Common Shares Issued \| shares	1,843
Common Share Value	$ 189,700,000
Cash Paid	398,300,000
Accrued Liability	50,000,000
Escrow Deposited	30,700,000
Recorded Earnout Payable	207,400,000
Total Recorded Purchase Price	876,100,000
Maximum Potential Earnout Payable	$ 387,900,000
Capsicum Reinsurance Brokers LLP (CRB) [Member]
Business Acquisition [Line Items]
Common Shares Issued \| shares	584
Common Share Value	$ 62,900,000
Cash Paid	64,500,000
Recorded Earnout Payable	129,900,000
Total Recorded Purchase Price	257,300,000
Maximum Potential Earnout Payable	209,100,000
Hanover Excess & Surplus, Inc. and Hanover Premium Finance, Inc. (HES) [Member]
Business Acquisition [Line Items]
Cash Paid	30,100,000
Escrow Deposited	3,000,000
Total Recorded Purchase Price	33,100,000
Maximum Potential Earnout Payable	$ 9,300,000
CRES Insurance Services, LLC (CRES) [Member]
Business Acquisition [Line Items]
Common Shares Issued \| shares	288
Common Share Value	$ 28,500,000
Cash Paid	1,500,000
Escrow Deposited	1,000,000
Recorded Earnout Payable	5,500,000
Total Recorded Purchase Price	36,500,000
Maximum Potential Earnout Payable	$ 7,300,000
Optimum Talent Inc. (OTI) [Member]
Business Acquisition [Line Items]
Common Shares Issued \| shares	102
Common Share Value	$ 11,100,000
Cash Paid	14,100,000
Escrow Deposited	3,400,000
Recorded Earnout Payable	14,000,000
Total Recorded Purchase Price	42,600,000
Maximum Potential Earnout Payable	21,100,000
Ashton Tiffany, LLC (AT) [Member]
Business Acquisition [Line Items]
Cash Paid	48,300,000
Accrued Liability	48,200,000
Recorded Earnout Payable	9,000,000
Total Recorded Purchase Price	105,500,000
Maximum Potential Earnout Payable	$ 20,000,000
Cool Insuring Agency, Inc. (CIA) [Member]
Business Acquisition [Line Items]
Common Shares Issued \| shares	406
Common Share Value	$ 48,400,000
Cash Paid	65,000,000
Escrow Deposited	7,200,000
Recorded Earnout Payable	8,500,000
Total Recorded Purchase Price	129,100,000
Maximum Potential Earnout Payable	$ 30,000,000
Harden & Associates, Inc. (HAI) [Member]
Business Acquisition [Line Items]
Common Shares Issued \| shares	49
Cash Paid	$ 95,600,000
Escrow Deposited	6,200,000
Recorded Earnout Payable	10,000,000
Total Recorded Purchase Price	111,800,000
Maximum Potential Earnout Payable	$ 22,500,000
Twenty Other Acquisitions [Member]
Business Acquisition [Line Items]
Common Shares Issued \| shares	414
Common Share Value	$ 38,800,000
Cash Paid	79,200,000
Accrued Liability	1,800,000
Escrow Deposited	9,900,000
Recorded Earnout Payable	30,500,000
Total Recorded Purchase Price	160,200,000
Maximum Potential Earnout Payable	$ 68,600,000

Business Combinations - Additio

Business Combinations - Additional Information (Detail)	Dec. 23, 2020USD ($)EmployeeOffice	Dec. 31, 2020USD ($)Entity	Dec. 31, 2019USD ($)Entity	Dec. 31, 2018USD ($)Entity	Dec. 31, 2020USD ($)Entity
Business Acquisition [Line Items]
Cash consideration		$ 398,300,000
Accrued liability		50,000,000			$ 50,000,000
Accretion of the discount on acquisition		32,500,000	$ 27,000,000	$ 18,800,000
Income (expense) related to net adjustments to estimated fair value of liability for earnout obligations		$ 65,400,000	$ 11,700,000	$ 9,200,000
Number of companies acquired \| Entity		135	116	112	583
Aggregate amount of maximum earnout obligations related to acquisitions		$ 1,128,100,000	$ 982,900,000
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet		592,200,000	565,000,000
Aggregate amount of earnout obligation expected settlement in cash		98,500,000			$ 98,500,000
Aggregate amount of earnout obligation expected settlement in cash or stock at option		493,700,000			493,700,000
Goodwill		359,600,000			359,600,000
Expiration lists		467,200,000			467,200,000
Non-compete agreements		11,400,000			11,400,000
Trade names		12,500,000			12,500,000
Write-off of amortizable intangible assets		51,700,000	100,000	$ 10,600,000
Total revenues		7,108,700,000	7,352,700,000
Brokerage Management [Member]
Business Acquisition [Line Items]
Goodwill		359,600,000			359,600,000
Expiration lists		467,200,000			467,200,000
Non-compete agreements		11,400,000			11,400,000
Trade names		12,500,000			12,500,000
Brokerage and Risk Management [Member]
Business Acquisition [Line Items]
Write-off of amortizable intangible assets		51,700,000	$ 100,000	$ 10,600,000
Brokerage [Member] \| Expiration Lists [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes		29,000,000			29,000,000
Brokerage [Member] \| Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes		600,000			600,000
Brokerage [Member] \| Trade Names [Member]
Business Acquisition [Line Items]
Business acquisition not deductible for income tax purposes		$ 0			0
Minimum [Member] \| Expiration Lists [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years		2 years
Minimum [Member] \| Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years		2 years
Minimum [Member] \| Trade Names [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years		2 years
Maximum [Member] \| Expiration Lists [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years		15 years
Maximum [Member] \| Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years		6 years
Maximum [Member] \| Trade Names [Member]
Business Acquisition [Line Items]
Estimated useful lives of intangibles assets, years		15 years
The Bollington Wilson Group [Member]
Business Acquisition [Line Items]
Percentage of voting interest	100.00%
Cash consideration	$ 330,000,000
Number of employees in the acquired company \| Employee	400
Number of operating offices in the acquired company \| Office	7
Ashton Tiffany, LLC (AT) [Member]
Business Acquisition [Line Items]
Cash consideration		$ 48,300,000
Accrued liability		48,200,000			48,200,000
Goodwill		14,800,000			14,800,000
Expiration lists		78,200,000			78,200,000
Non-compete agreements		5,800,000			5,800,000
Ashton Tiffany, LLC (AT) [Member] \| Common Stock [Member]
Business Acquisition [Line Items]
Accrued liability		$ 48,200,000			$ 48,200,000
2020 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Measurement Input, Discount Rate [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Measurement input		2.5			2.5
2020 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Measurement Input, Discount Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input		15			15
2020 Acquisitions [Member] \| Valuation, Income Approach [Member] \| Measurement Input, Discount Rate [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Measurement input		6			6
2020 Acquisitions [Member] \| Valuation, Income Approach [Member] \| Measurement Input, Discount Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input		9			9
2020 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Attrition rate		5.00%
2020 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Attrition rate		15.70%
2020 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Measurement input		1.5			1.5
2020 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input		4.1			4.1
2020 Acquisitions [Member] \| Valuation, Income Approach [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Measurement input		9			9
2020 Acquisitions [Member] \| Valuation, Income Approach [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input		13.5			13.5
2019 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Attrition rate		5.00%
2019 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Attrition rate		15.70%
2019 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Measurement input		1.5			1.5
2019 Acquisitions [Member] \| Valuation, Market Approach [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input		4.1			4.1
2019 Acquisitions [Member] \| Valuation, Income Approach [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Measurement input		9			9
2019 Acquisitions [Member] \| Valuation, Income Approach [Member] \| Measurement Input, Long-term Revenue Growth Rate [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Measurement input		13.5			13.5
Business Acquisition [Member]
Business Acquisition [Line Items]
Trade names		$ 12,500,000			$ 12,500,000
Annualized revenue of business acquisitions		251,400,000
Total revenues		52,700,000
Net earnings		5,200,000
Business Acquisition [Member] \| Brokerage [Member]
Business Acquisition [Line Items]
Expiration lists		467,200,000			467,200,000
Non-compete agreements		11,400,000			11,400,000
Deferred tax liability		$ 3,900,000			$ 3,900,000

Business Combinations - Summary

Business Combinations - Summary of Estimated Fair Values of Net Assets Acquired (Detail) $ in Millions	Dec. 31, 2020USD ($)
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash and restricted cash	$ 34
Other current assets	88
Fixed assets	3.2
Noncurrent assets	27.6
Goodwill	359.6
Expiration lists	467.2
Non-compete agreements	11.4
Trade names	12.5
Total assets acquired	1,003.5
Current liabilities	103.6
Noncurrent liabilities	23.8
Total liabilities assumed	127.4
Total net assets acquired	876.1
CRB [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Noncurrent assets	7.6
Goodwill	108.4
Expiration lists	133.7
Non-compete agreements	2.9
Trade names	4.7
Total assets acquired	257.3
Total net assets acquired	257.3
HES [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash and restricted cash	3.3
Other current assets	1
Noncurrent assets	0.8
Goodwill	19.1
Expiration lists	13.7
Non-compete agreements	0.1
Total assets acquired	38
Current liabilities	4.4
Noncurrent liabilities	0.5
Total liabilities assumed	4.9
Total net assets acquired	33.1
CRES [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash and restricted cash	4.3
Other current assets	12.4
Goodwill	21.3
Expiration lists	13.9
Trade names	0.3
Total assets acquired	52.2
Current liabilities	15.7
Total liabilities assumed	15.7
Total net assets acquired	36.5
OTI [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash and restricted cash	0.6
Other current assets	3
Fixed assets	0.9
Noncurrent assets	6.7
Goodwill	25.4
Expiration lists	18.3
Non-compete agreements	0.4
Total assets acquired	55.3
Current liabilities	5.2
Noncurrent liabilities	7.5
Total liabilities assumed	12.7
Total net assets acquired	42.6
CIA [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash and restricted cash	4.2
Other current assets	28.8
Fixed assets	0.1
Noncurrent assets	0.9
Goodwill	58.9
Expiration lists	56.2
Non-compete agreements	0.8
Trade names	7.5
Total assets acquired	157.4
Current liabilities	28.1
Noncurrent liabilities	0.2
Total liabilities assumed	28.3
Total net assets acquired	129.1
HAI [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash and restricted cash	2.3
Other current assets	9
Fixed assets	1.1
Noncurrent assets	6.4
Goodwill	45.7
Expiration lists	62.5
Non-compete agreements	0.7
Total assets acquired	127.7
Current liabilities	9.5
Noncurrent liabilities	6.4
Total liabilities assumed	15.9
Total net assets acquired	111.8
AT [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash and restricted cash	6
Other current assets	8.6
Fixed assets	0.5
Noncurrent assets	2.1
Goodwill	14.8
Expiration lists	78.2
Non-compete agreements	5.8
Total assets acquired	116
Current liabilities	8.4
Noncurrent liabilities	2.1
Total liabilities assumed	10.5
Total net assets acquired	105.5
Twenty Other Acquisitions [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Cash and restricted cash	13.3
Other current assets	25.2
Fixed assets	0.6
Noncurrent assets	3.1
Goodwill	66
Expiration lists	90.7
Non-compete agreements	0.7
Total assets acquired	199.6
Current liabilities	32.3
Noncurrent liabilities	7.1
Total liabilities assumed	39.4
Total net assets acquired	$ 160.2

Business Combinations - Summa_2

Business Combinations - Summary of Unaudited Pro Forma Historical Results (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Business Combinations [Abstract]
Total revenues	$ 7,108.7	$ 7,352.7
Net earnings attributable to controlling interests	$ 817.6	$ 670.5
Basic net earnings per share	$ 4.26	$ 3.57
Diluted net earnings per share	$ 4.17	$ 3.49

Contracts with Customers - Summ

Contracts with Customers - Summary of Unbilled Receivables, Contract Assets and Contract Liabilities from Contracts with Customers (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Contract With Customer Asset And Liability [Abstract]
Unbilled receivables	$ 603.1	$ 556.4
Deferred contract costs	102	98.3
Deferred revenue	$ 541.3	$ 503.8	$ 457.7

Contracts with Customers - Su_2

Contracts with Customers - Summary of Changes in Deferred Revenue Balances (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Deferred Revenue Arrangement [Line Items]
Deferred revenue beginning balance	$ 503.8	$ 457.7
Incremental deferred revenue	374	364.3
Revenue recognized during the year included in deferred revenue of prior year	(382.3)	(349.5)
Net change in collected billings/deposits received from customers	25.6	(1.1)
Impact of changes in foreign exchange rates	10.3	1.8
Deferred revenue recognized from business acquisitions	9.9	30.6
Deferred revenue ending balance	541.3	503.8
Brokerage [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue beginning balance	337.2	284.7
Incremental deferred revenue	282.7	254.7
Revenue recognized during the year included in deferred revenue of prior year	(283.1)	(227.5)
Net change in collected billings/deposits received from customers	(0.7)	(6.7)
Impact of changes in foreign exchange rates	8.7	1.4
Deferred revenue recognized from business acquisitions	9.9	30.6
Deferred revenue ending balance	354.7	337.2
Risk Management [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue beginning balance	166.6	173
Incremental deferred revenue	91.3	109.6
Revenue recognized during the year included in deferred revenue of prior year	(99.2)	(122)
Net change in collected billings/deposits received from customers	26.3	5.6
Impact of changes in foreign exchange rates	1.6	0.4
Deferred revenue ending balance	$ 186.6	$ 166.6

Contracts with Customers - Addi

Contracts with Customers - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Revenue From Contract With Customer [Abstract]
Remaining performance obligations	$ 541.3
Deferred contract costs	102	$ 98.3
Amortization of deferred contract costs	$ 388.4	$ 355.9

Contracts with Customers - Su_3

Contracts with Customers - Summary of Expected Revenue Related to Performance Obligations (Detail) $ in Millions	Dec. 31, 2020USD ($)
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 541.3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 451.2
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 54.8
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 15.6
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 7.1
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2025-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 4.4
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2026-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 8.2
Remaining performance obligation, expected timing of satisfaction, period
Brokerage [Member]
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 354.7
Brokerage [Member] \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 328.4
Remaining performance obligation, expected timing of satisfaction, period	1 year
Brokerage [Member] \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 23.6
Remaining performance obligation, expected timing of satisfaction, period	1 year
Brokerage [Member] \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 1.4
Remaining performance obligation, expected timing of satisfaction, period	1 year
Brokerage [Member] \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 0.6
Remaining performance obligation, expected timing of satisfaction, period	1 year
Brokerage [Member] \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2025-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 0.4
Remaining performance obligation, expected timing of satisfaction, period	1 year
Brokerage [Member] \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2026-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 0.3
Remaining performance obligation, expected timing of satisfaction, period
Risk Management [Member]
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 186.6
Risk Management [Member] \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 122.8
Remaining performance obligation, expected timing of satisfaction, period	1 year
Risk Management [Member] \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 31.2
Remaining performance obligation, expected timing of satisfaction, period	1 year
Risk Management [Member] \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 14.2
Remaining performance obligation, expected timing of satisfaction, period	1 year
Risk Management [Member] \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 6.5
Remaining performance obligation, expected timing of satisfaction, period	1 year
Risk Management [Member] \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2025-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 4
Remaining performance obligation, expected timing of satisfaction, period	1 year
Risk Management [Member] \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2026-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 7.9
Remaining performance obligation, expected timing of satisfaction, period

Contracts with Customers - Su_4

Contracts with Customers - Summary of Expected Revenue Related to Performance Obligations 1 (Detail) $ in Millions	Dec. 31, 2020USD ($)
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 541.3
Brokerage [Member]
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	354.7
Risk Management [Member]
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 186.6

Other Financial Data - Summary

Other Financial Data - Summary of Major Classes of Other Current Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Premium finance advances and loans	$ 442.7	$ 388.1
Accrued supplemental, direct bill and other receivables	361.7	369.1
Refined coal production related receivables	95.4	103.4
Deferred contract costs	102	98.3
Prepaid expenses	112.1	115.5
Total other current assets	$ 1,113.9	$ 1,074.4

Fixed Assets - Summary of Fixed

Fixed Assets - Summary of Fixed Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment Useful Life And Values [Abstract]
Office equipment	$ 33	$ 32.6
Furniture and fixtures	138.3	126
Leasehold improvements	166	150.2
Computer equipment	214.2	176.3
Land and buildings - corporate headquarters	145.1	144.9
Software	452.2	392.3
Other	16.7	19
Work in process	14.1	18
Gross fixed assets	1,179.6	1,059.3
Accumulated depreciation	(728.9)	(591.9)
Net fixed assets	$ 450.7	$ 467.4

Intangible Assets - Carrying Am

Intangible Assets - Carrying Amount of Goodwill Allocated by Domestic and Foreign Operations (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Total goodwill - net	$ 6,127	$ 5,618.5	$ 4,625.6
Unites States [Member]
Goodwill [Line Items]
Total goodwill - net	3,433	3,196.9
United Kingdom [Member]
Goodwill [Line Items]
Total goodwill - net	1,343.4	1,190.7
Canada [Member]
Goodwill [Line Items]
Total goodwill - net	492.9	454.4
Australia [Member]
Goodwill [Line Items]
Total goodwill - net	473.6	427
New Zealand [Member]
Goodwill [Line Items]
Total goodwill - net	232.6	218.1
Other Foreign [Member]
Goodwill [Line Items]
Total goodwill - net	151.5	131.4
Brokerage [Member]
Goodwill [Line Items]
Total goodwill - net	6,053.6	5,548.9	4,573.6
Brokerage [Member] \| Unites States [Member]
Goodwill [Line Items]
Total goodwill - net	3,399.8	3,163.8
Brokerage [Member] \| United Kingdom [Member]
Goodwill [Line Items]
Total goodwill - net	1,328.3	1,177.8
Brokerage [Member] \| Canada [Member]
Goodwill [Line Items]
Total goodwill - net	492.9	454.4
Brokerage [Member] \| Australia [Member]
Goodwill [Line Items]
Total goodwill - net	462.1	416.5
Brokerage [Member] \| New Zealand [Member]
Goodwill [Line Items]
Total goodwill - net	221.9	208
Brokerage [Member] \| Other Foreign [Member]
Goodwill [Line Items]
Total goodwill - net	148.6	128.4
Risk Management [Member]
Goodwill [Line Items]
Total goodwill - net	70.5	66.6	49.3
Risk Management [Member] \| Unites States [Member]
Goodwill [Line Items]
Total goodwill - net	33.2	33.1
Risk Management [Member] \| United Kingdom [Member]
Goodwill [Line Items]
Total goodwill - net	15.1	12.9
Risk Management [Member] \| Australia [Member]
Goodwill [Line Items]
Total goodwill - net	11.5	10.5
Risk Management [Member] \| New Zealand [Member]
Goodwill [Line Items]
Total goodwill - net	10.7	10.1
Corporate [Member]
Goodwill [Line Items]
Total goodwill - net	2.9	3	$ 2.7
Corporate [Member] \| Other Foreign [Member]
Goodwill [Line Items]
Total goodwill - net	$ 2.9	$ 3

Intangible Assets - Changes in

Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Beginning Balance	$ 5,618.5	$ 4,625.6
Goodwill acquired during the year	359.6	975.7
Goodwill adjustments related to appraisals and other acquisition adjustments	31.5
Goodwill written-off related to sales of business		(7.2)
Foreign currency translation adjustments during the year	117.4	24.4
Ending Balance	6,127	5,618.5
Brokerage [Member]
Goodwill [Line Items]
Beginning Balance	5,548.9	4,573.6
Goodwill acquired during the year	359.6	958.4
Goodwill adjustments related to appraisals and other acquisition adjustments	29.8	0.2
Goodwill written-off related to sales of business		(7.2)
Foreign currency translation adjustments during the year	115.3	23.9
Ending Balance	6,053.6	5,548.9
Risk Management [Member]
Goodwill [Line Items]
Beginning Balance	66.6	49.3
Goodwill acquired during the year		16.9
Goodwill adjustments related to appraisals and other acquisition adjustments	1.7	(0.2)
Foreign currency translation adjustments during the year	2.2	0.6
Ending Balance	70.5	66.6
Corporate [Member]
Goodwill [Line Items]
Beginning Balance	3	2.7
Goodwill acquired during the year		0.4
Foreign currency translation adjustments during the year	(0.1)	(0.1)
Ending Balance	$ 2.9	$ 3

Intangible Assets - Major Class

Intangible Assets - Major Classes of Amortizable Intangible Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, net	$ 2,399.9	$ 2,318.7
Expiration Lists [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	4,753.2	4,246
Accumulated amortization	(2,436.7)	(2,004.3)
Amortizable intangible assets, net	2,316.5	2,241.7
Non-Compete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	75.9	68.4
Accumulated amortization	(57.8)	(52.5)
Amortizable intangible assets, net	18.1	15.9
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	107.8	91.8
Accumulated amortization	(42.5)	(30.7)
Amortizable intangible assets, net	$ 65.3	$ 61.1

Intangible Assets - Estimated A

Intangible Assets - Estimated Aggregate Amortization Expense (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Goodwill And Intangible Assets Disclosure [Abstract]
2021	$ 378.4
2022	352.3
2023	327.1
2024	291.3
2025	251.3
Thereafter	799.5
Amortizable intangible assets, net	$ 2,399.9	$ 2,318.7

Credit and Other Debt Agreeme_3

Credit and Other Debt Agreements - Summary of Corporate and Other Debt (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Semi-annual payments of interest	$ 4,551.6	$ 4,613.6
Less unamortized debt acquisition costs on Note Purchase Agreements	(7)	(6.9)
Semi-annual payments of interest, Net	4,544.6	4,606.7
Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	4,348	3,923
Fixed Rate of 3.48%, Balloon Due June 24, 2020 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest		50
Fixed Rate of 3.99%, Balloon Due July 10, 2020 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest		50
Fixed Rate of 5.18%, Balloon Due February 10, 2021 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	75	75
Fixed Rate of 3.69%, Balloon Due June 14, 2022 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	200	200
Fixed Rate of 5.49%, Balloon Due February 10, 2023 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50	50
Fixed Rate of 4.13%, Balloon Due June 24, 2023 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	200	200
Floating Rate of 1.65% LIBOR Plus Balloon Due August 2, 2023 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest		50
Fixed Rate of 4.72%, Balloon due February 13, 2024 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	100	100
Fixed Rate of 4.58%, Balloon Due February 27, 2024 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	325	325
Floating Interest Rate of 1.40% LIBOR Plus Balloon Due June 13, 2024 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50	50
Fixed Rate of 4.31%, Balloon Due June 24, 2025 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	200	200
Fixed Rate of 4.85%, Balloon due February 13, 2026 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	140	140
Fixed Rate of 4.73%, Balloon Due February 27, 2026 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	175	175
Fixed Rate of 4.40%, Balloon Due June 2, 2026 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	175	175
Fixed Rate of 4.36%, Balloon Due June 24, 2026 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	150	150
Fixed Rate of 3.75%, Balloon Due January 30, 2027 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	30
Fixed Rate of 4.09%, Balloon Due June 27, 2027 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	125	125
Fixed Rate of 4.09%, Balloon Due August 2, 2027 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	125	125
Fixed Rate of 4.14%, Balloon Due August 4, 2027 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	98	98
Fixed Rate of 3.46%, Balloon Due December 1, 2027 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	100	100
Fixed Rate of 4.55%, Balloon Due June 2, 2028 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	75	75
Fixed Rate of 4.34%, Balloon due June 13, 2028 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	125	125
Fixed Rate of 5.04%, Balloon due February 13, 2029 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	100	100
Fixed Rate of 4.98%, Balloon Due February 27, 2029 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	100	100
Fixed Rate of 4.19%, Balloon Due June 27, 2029 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50	50
Fixed Rate of 4.19%, Balloon Due August 2, 2029 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50	50
Fixed Rate of 3.48%, Balloon Due December 2, 2029 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	50	50
Fixed Rate of 3.99%, Balloon Due January 30, 2030 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	341
Fixed Rate of 4.44%, Balloon Due June 13, 2030 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	125	125
Fixed Rate of 5.14%, Balloon due March 13, 2031 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	180	180
Fixed Rate of 4.70%, Balloon Due June 2, 2031 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	25	25
Fixed Rate of 4.09%, Balloon Due January 30, 2032 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	69
Fixed Rate of 4.34%, Balloon Due June 27, 2032 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	75	75
Fixed Rate of 4.34%, Balloon Due August 2, 2032 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	75	75
Fixed Rate of 4.59%, Balloon due June 13, 2033 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	125	125
Fixed Rate of 5.29%, balloon due March 13, 2034 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	40	40
Fixed Rate of 4.48%, Balloon Due June 12, 2034 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	175	175
Fixed Rate of 4.24%, Balloon Due January 30, 2035 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	79
Fixed Rate of 4.69%, Balloon Due June 13, 2038 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	75	75
Fixed Rate of 5.45%, balloon due March 13, 2039 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	40	40
Fixed Rate of 4.49%, Balloon Due January 30, 2040 [Member] \| Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	56
Prime or LIBOR Plus up to 1.45%, Expires June 7, 2024 [Member] \| Multi Currency Credit Agreement [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest		520
Interbank Rates Plus 1.400% Expires September 15, 2022 [Member] \| AUD Denominated Tranche [Member] \| Facility B [Member] \| Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	193.1	142.1
Interbank Rates Plus 0.730% Expires September 15, 2022 [Member] \| AUD Denominated Tranche [Member] \| Facility C and D [Member] \| Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest		18.8
Interbank Rates Plus 0.940% Expires September 15, 2022 [Member] \| NZD Denominated Tranche [Member] \| Facility C and D [Member] \| Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	10.5	9.7
Interbank Rates Expires September 15, 2022 [Member] \| Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Semi-annual payments of interest	$ 203.6	$ 170.6

Credit and Other Debt Agreeme_4

Credit and Other Debt Agreements - Summary of Corporate and Other Debt (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Periodic payments of interest and principal, expiry date	Sep. 15, 2022	Sep. 15, 2022
Fixed Rate of 3.48%, Balloon Due June 24, 2020 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest		3.48%
Periodic payments of interest and principal, expiry date		Jun. 24, 2020
Fixed Rate of 3.99%, Balloon Due July 10, 2020 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest		3.99%
Periodic payments of interest and principal, expiry date		Jul. 10, 2020
Fixed Rate of 5.18%, Balloon Due February 10, 2021 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.18%	5.18%
Periodic payments of interest and principal, expiry date	Feb. 10, 2021	Feb. 10, 2021
Fixed Rate of 3.69%, Balloon Due June 14, 2022 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.69%	3.69%
Periodic payments of interest and principal, expiry date	Jun. 14, 2022	Jun. 14, 2022
Fixed Rate of 5.49%, Balloon Due February 10, 2023 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.49%	5.49%
Periodic payments of interest and principal, expiry date	Feb. 10, 2023	Feb. 10, 2023
Fixed Rate of 4.13%, Balloon Due June 24, 2023 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.13%	4.13%
Periodic payments of interest and principal, expiry date	Jun. 24, 2023	Jun. 24, 2023
Floating Rate of 1.65% LIBOR Plus Balloon Due August 2, 2023 [Member]
Debt Instrument [Line Items]
Periodic payments of interest and principal, expiry date		Aug. 2, 2023
Quarterly payments of interest rate		1.65%
Quarterly payments of interest, description	90 day LIBOR
Debt instrument, prepayment date		Nov. 3, 2020
Fixed Rate of 4.72%, Balloon due February 13, 2024 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.72%	4.72%
Periodic payments of interest and principal, expiry date	Feb. 13, 2024	Feb. 13, 2024
Fixed Rate of 4.58%, Balloon Due February 27, 2024 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.58%	4.58%
Periodic payments of interest and principal, expiry date	Feb. 27, 2024	Feb. 27, 2024
Floating Interest Rate of 1.40% LIBOR Plus Balloon Due June 13, 2024 [Member]
Debt Instrument [Line Items]
Periodic payments of interest and principal, expiry date	Jun. 13, 2024	Jun. 13, 2024
Quarterly payments of interest rate	1.40%	1.40%
Quarterly payments of interest, description	90 day LIBOR plus
Fixed Rate of 4.31%, Balloon Due June 24, 2025 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.31%	4.31%
Periodic payments of interest and principal, expiry date	Jun. 24, 2025	Jun. 24, 2025
Fixed Rate of 4.85%, Balloon due February 13, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.85%	4.85%
Periodic payments of interest and principal, expiry date	Feb. 13, 2026	Feb. 13, 2026
Fixed Rate of 4.73%, Balloon Due February 27, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.73%	4.73%
Periodic payments of interest and principal, expiry date	Feb. 27, 2026	Feb. 27, 2026
Fixed Rate of 4.40%, Balloon Due June 2, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.40%	4.40%
Periodic payments of interest and principal, expiry date	Jun. 2, 2026	Jun. 2, 2026
Fixed Rate of 4.36%, Balloon Due June 24, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.36%	4.36%
Periodic payments of interest and principal, expiry date	Jun. 24, 2026	Jun. 24, 2026
Fixed Rate of 3.75%, Balloon Due January 30, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.75%
Periodic payments of interest and principal, expiry date	Jan. 30, 2027
Fixed Rate of 4.09%, Balloon Due June 27, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.09%	4.09%
Periodic payments of interest and principal, expiry date	Jun. 27, 2027	Jun. 27, 2027
Fixed Rate of 4.09%, Balloon Due August 2, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.09%	4.09%
Periodic payments of interest and principal, expiry date	Aug. 2, 2027	Aug. 2, 2027
Fixed Rate of 4.14%, Balloon Due August 4, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.14%	4.14%
Periodic payments of interest and principal, expiry date	Aug. 4, 2027	Aug. 4, 2027
Fixed Rate of 3.46%, Balloon Due December 1, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.46%	3.46%
Periodic payments of interest and principal, expiry date	Dec. 1, 2027	Dec. 1, 2027
Fixed Rate of 4.55%, Balloon Due June 2, 2028 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.55%	4.55%
Periodic payments of interest and principal, expiry date	Jun. 2, 2028	Jun. 2, 2028
Fixed Rate of 4.34%, Balloon due June 13, 2028 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.34%	4.34%
Periodic payments of interest and principal, expiry date	Jun. 13, 2028	Jun. 13, 2028
Fixed Rate of 5.04%, Balloon due February 13, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.04%	5.04%
Periodic payments of interest and principal, expiry date	Feb. 13, 2029	Feb. 13, 2029
Fixed Rate of 4.98%, Balloon Due February 27, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.98%	4.98%
Periodic payments of interest and principal, expiry date	Feb. 27, 2029	Feb. 27, 2029
Fixed Rate of 4.19%, Balloon Due June 27, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.19%	4.19%
Periodic payments of interest and principal, expiry date	Jun. 27, 2029	Jun. 27, 2029
Fixed Rate of 4.19%, Balloon Due August 2, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.19%	4.19%
Periodic payments of interest and principal, expiry date	Aug. 2, 2029	Aug. 2, 2029
Fixed Rate of 3.48%, Balloon Due December 2, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.48%	3.48%
Periodic payments of interest and principal, expiry date	Dec. 2, 2029	Dec. 2, 2029
Fixed Rate of 3.99%, Balloon Due January 30, 2030 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.99%
Periodic payments of interest and principal, expiry date	Jan. 30, 2030
Fixed Rate of 4.44%, Balloon Due June 13, 2030 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.44%	4.44%
Periodic payments of interest and principal, expiry date	Jun. 13, 2030	Jun. 13, 2030
Fixed Rate of 5.14%, Balloon due March 13, 2031 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.14%	5.14%
Periodic payments of interest and principal, expiry date	Mar. 13, 2031	Mar. 13, 2031
Fixed Rate of 4.70%, Balloon Due June 2, 2031 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.70%	4.70%
Periodic payments of interest and principal, expiry date	Jun. 2, 2031	Jun. 2, 2031
Fixed Rate of 4.09%, Balloon Due January 30, 2032 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.09%
Periodic payments of interest and principal, expiry date	Jan. 30, 2032
Fixed Rate of 4.34%, Balloon Due June 27, 2032 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.34%	4.34%
Periodic payments of interest and principal, expiry date	Jun. 27, 2032	Jun. 27, 2032
Fixed Rate of 4.34%, Balloon Due August 2, 2032 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.34%	4.34%
Periodic payments of interest and principal, expiry date	Aug. 2, 2032	Aug. 2, 2032
Fixed Rate of 4.59%, Balloon due June 13, 2033 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.59%	4.59%
Periodic payments of interest and principal, expiry date	Jun. 13, 2033	Jun. 13, 2033
Fixed Rate of 5.29%, balloon due March 13, 2034 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.29%	5.29%
Periodic payments of interest and principal, expiry date	Mar. 13, 2034	Mar. 13, 2034
Fixed Rate of 4.48%, Balloon Due June 12, 2034 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.48%	4.48%
Periodic payments of interest and principal, expiry date	Jun. 12, 2034	Jun. 12, 2034
Fixed Rate of 4.69%, Balloon Due June 13, 2038 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.69%	4.69%
Periodic payments of interest and principal, expiry date	Jun. 13, 2038	Jun. 13, 2038
Fixed Rate of 5.45%, balloon due March 13, 2039 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.45%	5.45%
Periodic payments of interest and principal, expiry date	Mar. 13, 2039	Mar. 13, 2039
Fixed Rate of 4.24%, Balloon Due January 30, 2035 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.24%
Periodic payments of interest and principal, expiry date	Jan. 30, 2035
Prime or LIBOR Plus up to 1.45%, Expires June 7, 2024 [Member] \| Credit Agreement [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest		1.45%
Periodic payments of interest and principal, expiry date		Jun. 7, 2024
Fixed Rate of 4.49%, Balloon Due January 30, 2040 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.49%
Periodic payments of interest and principal, expiry date	Jan. 30, 2040
Facility B [Member] \| Interbank Rates Plus 1.400% Expires September 15, 2022 [Member] \| Premium Financing Debt Facility [Member] \| AUD Denominated Tranche [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	1.40%	1.40%
Facility C and D [Member] \| Interbank Rates Plus 0.730% Expires September 15, 2022 [Member] \| Premium Financing Debt Facility [Member] \| AUD Denominated Tranche [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest		0.73%
Facility C and D [Member] \| Interbank Rates Plus 0.940% Expires September 15, 2022 [Member] \| Premium Financing Debt Facility [Member] \| NZD Denominated Tranche [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	0.94%	0.94%

Credit and Other Debt Agreeme_5

Credit and Other Debt Agreements - Note Purchase Agreements - Additional Information (Detail) - USD ($) $ in Millions	Jan. 30, 2020	Dec. 02, 2019	Jun. 12, 2019	Feb. 13, 2019	Dec. 31, 2020	Dec. 31, 2019
Fixed Rate of 4.72%, Balloon due February 13, 2024 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 100
Debt instrument, interest rate					4.72%	4.72%
Debt instrument, due date					2024
Fixed Rate of 4.85%, Balloon due February 13, 2026 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 140
Debt instrument, interest rate					4.85%	4.85%
Debt instrument, due date					2026
Fixed Rate of 5.04%, Balloon due February 13, 2029 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 100
Debt instrument, interest rate					5.04%	5.04%
Debt instrument, due date					2029
Fixed Rate of 5.14%, Balloon due March 13, 2031 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 180
Debt instrument, interest rate					5.14%	5.14%
Debt instrument, due date					2031
Fixed Rate of 5.29%, balloon due March 13, 2034 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 40
Debt instrument, interest rate					5.29%	5.29%
Debt instrument, due date					2034
Fixed Rate of 5.45%, balloon due March 13, 2039 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 40
Debt instrument, interest rate					5.45%	5.45%
Debt instrument, due date					2039
Fixed Rate of 3.75% Senior Notes Due in 2027 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 30
Debt instrument, interest rate					3.75%
Debt instrument, due date					2027
Fixed Rate of 3.99% Senior Notes Due in 2030 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 341
Debt instrument, interest rate					3.99%
Debt instrument, due date					2030
Fixed Rate of 4.09% Senior Notes Due in 2032 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 69
Debt instrument, interest rate					4.09%
Debt instrument, due date					2032
Fixed Rate of 4.24% Senior Notes Due in 2035 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 79
Debt instrument, interest rate					4.24%
Debt instrument, due date					2035
Fixed Rate of 4.49% Senior Notes Due in 2040 [Member]
Debt Instrument [Line Items]
Notes issued and sold					$ 56
Debt instrument, interest rate					4.49%
Debt instrument, due date					2040
Note Purchase Agreements [Member]
Debt Instrument [Line Items]
Realized a cash gain on hedging transaction	$ 8.9		$ 5.2	$ 1.2
Derivative instrument, term	10 years
Amount payable to redeem the notes, percent of the principal amount					100.00%
Discount rate used to compute the remaining scheduled payments of principal and interest					U.S. Treasury yield plus 0.5
Note Purchase Agreements [Member] \| Senior Unsecured Notes [Member] \| Private Placement [Member]
Debt Instrument [Line Items]
Notes issued and sold				600
Note Purchase Agreements [Member] \| Fixed Rate Senior Unsecured Notes [Member] \| Private Placement [Member] \| Tranche One [Member]
Debt Instrument [Line Items]
Notes issued and sold				340
Note Purchase Agreements [Member] \| Fixed Rate Senior Unsecured Notes [Member] \| Private Placement [Member] \| Tranche Two [Member]
Debt Instrument [Line Items]
Notes issued and sold				$ 260
Note Purchase Agreements [Member] \| Unsecured Notes [Member]
Debt Instrument [Line Items]
Weighted average interest rate of notes				5.04%
Note Purchase Agreements [Member] \| Unsecured Notes [Member] \| Private Placement [Member]
Debt Instrument [Line Items]
Notes issued and sold	$ 575	$ 50	$ 175
Weighted average maturity of notes	11 years 8 months 12 days
Weighted average interest rate of notes	4.23%	3.48%
Debt instrument, interest rate			4.48%
Debt instrument, due date		2029	2034
Note Purchase Agreements [Member] \| Unsecured Notes [Member] \| Private Placement [Member] \| Weighted Average [Member]
Debt Instrument [Line Items]
Weighted average maturity of notes				10 years 1 month 6 days
Note Purchase Agreements [Member] \| Series K Notes [Member]
Debt Instrument [Line Items]
Notes issued and sold			$ 50
Weighted average interest rate of notes			4.68%
Note Purchase Agreements [Member] \| Series C Notes [Member]
Debt Instrument [Line Items]
Notes issued and sold		$ 50

Credit and Other Debt Agreeme_6

Credit and Other Debt Agreements - Credit Agreement - Additional Information (Detail) $ in Millions	Jun. 07, 2019USD ($)Institution	Apr. 08, 2016USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2020NZD ($)	Dec. 31, 2020AUD ($)	Dec. 31, 2020NZD ($)	Dec. 31, 2020AUD ($)	Sep. 16, 2020AUD ($)	Dec. 31, 2019USD ($)
Debt Instrument [Line Items]
Liabilities			$ 16,098,700,000						$ 14,419,300,000
Long-term debt			19,600,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, amount outstanding			$ 203,600,000
Interest rate for facility			The interest rates on Facility B are Interbank rates, which vary by tranche, duration and currency, plus a margin of 1.400% and 1.750% for the AU$ and NZ$ tranches, respectively. The interest rates on Facilities C and D are 30 day Interbank rates, plus a margin of 0.730% and 0.940% for the AU$ and NZ$ tranches, respectively. The annual fee for Facility B is 0.63% and 0.7875% for the undrawn commitments for the AU$ and NZ$ tranches, respectively. The annual fee for Facility C is 0.67% and for Facility D is 0.86% of the total commitments of the facilities	The interest rates on Facility B are Interbank rates, which vary by tranche, duration and currency, plus a margin of 1.400% and 1.750% for the AU$ and NZ$ tranches, respectively. The interest rates on Facilities C and D are 30 day Interbank rates, plus a margin of 0.730% and 0.940% for the AU$ and NZ$ tranches, respectively. The annual fee for Facility B is 0.63% and 0.7875% for the undrawn commitments for the AU$ and NZ$ tranches, respectively. The annual fee for Facility C is 0.67% and for Facility D is 0.86% of the total commitments of the facilities	The interest rates on Facility B are Interbank rates, which vary by tranche, duration and currency, plus a margin of 1.400% and 1.750% for the AU$ and NZ$ tranches, respectively. The interest rates on Facilities C and D are 30 day Interbank rates, plus a margin of 0.730% and 0.940% for the AU$ and NZ$ tranches, respectively. The annual fee for Facility B is 0.63% and 0.7875% for the undrawn commitments for the AU$ and NZ$ tranches, respectively. The annual fee for Facility C is 0.67% and for Facility D is 0.86% of the total commitments of the facilities
Debt instrument fair value amount			$ 203,600,000
Revolving Credit Facility [Member] \| Before Amendment [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity								$ 245,000,000
Revolving Credit Facility [Member] \| After Amendment [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity								$ 310,000,000
Multi Currency Credit Agreement [Member]
Debt Instrument [Line Items]
Number of financial institutions entered in unsecured multicurrency credit agreement \| Institution	15
Periodic payments of interest and principal, expiry date	Jun. 7, 2024	Apr. 8, 2021
Line of credit facility, maximum borrowing capacity	$ 1,200,000,000	$ 800,000,000
Line of credit facility, maximum amount outstanding during period			1,700,000,000
Debt acquisition costs			2,500,000
Estimated fair value of outstanding borrowings			$ 0
Multi Currency Credit Agreement [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rates on base rate loans			0.00%	0.00%	0.00%
Fixed rate over LIBOR			0.85%	0.85%	0.85%
Annual facility fee of revolving credit facility			0.15%	0.15%	0.15%
Multi Currency Credit Agreement [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rates on base rate loans			0.45%	0.45%	0.45%
Fixed rate over LIBOR			1.45%	1.45%	1.45%
Annual facility fee of revolving credit facility			0.30%	0.30%	0.30%
Multi Currency Credit Agreement [Member] \| Swing Loan [Member]
Debt Instrument [Line Items]
Long-term debt, gross			$ 75,000,000
Multi Currency Credit Agreement [Member] \| Standby Letters of Credit [Member]
Debt Instrument [Line Items]
Long-term debt, gross			75,000,000
Line of credit facility, amount outstanding			17,400,000
Liabilities			17,500,000
Line of credit facility, fair value of amount outstanding			0
Line of credit facility, remaining borrowing capacity			$ 1,182,600,000
Credit Facility Two [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, amount outstanding						$ 0	$ 255,000,000
Line of credit facility, remaining borrowing capacity						25	5,000,000
Net borrowings on premium financing debt facility				$ 25	$ 260,000,000
Credit Facility Three [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, amount outstanding							0
Net borrowings on premium financing debt facility					$ 50,000,000
Annual fee percentage			0.67%	0.67%	0.67%
Credit Facility Four [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, amount outstanding						14.9
Line of credit facility, remaining borrowing capacity						$ 0.1	$ 50,000,000
Net borrowings on premium financing debt facility				$ 15
Annual fee percentage			0.86%	0.86%	0.86%
AUD Denominated Tranche [Member] \| Revolving Credit Facility [Member] \| Facility B [Member]
Debt Instrument [Line Items]
Additional margin percentage on interest rate			1.40%	1.40%	1.40%
Annual fee percentage			0.63%	0.63%	0.63%
AUD Denominated Tranche [Member] \| Revolving Credit Facility [Member] \| Facility C and D [Member]
Debt Instrument [Line Items]
Additional margin percentage on interest rate			0.73%	0.73%	0.73%
NZD Denominated Tranche [Member] \| Revolving Credit Facility [Member] \| Facility B [Member]
Debt Instrument [Line Items]
Additional margin percentage on interest rate			1.75%	1.75%	1.75%
Annual fee percentage			0.7875%	0.7875%	0.7875%
NZD Denominated Tranche [Member] \| Revolving Credit Facility [Member] \| Facility C and D [Member]
Debt Instrument [Line Items]
Additional margin percentage on interest rate			0.94%	0.94%	0.94%
Note Purchase Agreements [Member] \| Level 3 [Member]
Debt Instrument [Line Items]
Line of credit facility, fair value of amount outstanding			$ 5,018,900,000
Long-term debt			$ 4,348,000,000

Earnings Per Share - Computatio

Earnings Per Share - Computation of Basic and Diluted Net EPS (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net earnings attributable to controlling interests	$ 142.2	$ 176.6	$ 153.7	$ 346.3	$ 98.5	$ 126.1	$ 110.1	$ 334.1	$ 818.8	$ 668.8	$ 633.5
Weighted average number of common shares outstanding									191	186	182.7
Dilutive effect of stock options using the treasury stock method									4	4.1	3.5
Weighted average number of common and common equivalent shares outstanding									195	190.1	186.2
Basic net earnings per share	$ 0.74	$ 0.92	$ 0.81	$ 1.83	$ 0.53	$ 0.68	$ 0.59	$ 1.81	$ 4.29	$ 3.60	$ 3.47
Diluted net earnings per share	$ 0.72	$ 0.90	$ 0.79	$ 1.79	$ 0.51	$ 0.66	$ 0.58	$ 1.77	$ 4.20	$ 3.52	$ 3.40

Earnings Per Share - Additional

Earnings Per Share - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Anti-dilutive stock-based awards shares outstanding	0	1,000,000	1,000,000

Stock Option Plans - Additional

Stock Option Plans - Additional information (Detail) - USD ($) $ / shares in Units, $ in Millions	Mar. 12, 2020	Mar. 14, 2019	Mar. 15, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock Option Plans [Line Items]
Compensation expense related to stock option grants				$ 13.6	$ 14	$ 13.7
Total intrinsic value of options exercised				106.4	$ 54.2	$ 77.9
Total unrecognized compensation cost related to nonvested options				$ 28.3
Weighted average period, years				4 years
Black-Scholes Option Pricing Model [Member]
Stock Option Plans [Line Items]
Weighted average fair value per option for all options				$ 9.99	$ 10.71	$ 9.27
Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Maximum number of shares available				2,300,000
Shares available for grant				11,400,000
Long Term Incentive Plan [Member] \| Maximum [Member]
Stock Option Plans [Line Items]
Minimum exercise price of stock options, percent of fair market value of a share of common stock on the date of grant				100.00%
Maximum period for the exercise of stock options, years				7 years	7 years	7 years
Long Term Incentive Plan [Member] \| Minimum [Member]
Stock Option Plans [Line Items]
Period of service from grant date stock options awarded not subject to forfeiture				2 years	2 years	2 years
Long Term Incentive Plan [Member] \| Minimum [Member] \| Executive Officer [Member]
Stock Option Plans [Line Items]
Minimum age of employee with not subject to award forfeiture on condition compliance				55 years	55 years	55 years
2017 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Number Of Periods Options Expire				7 years
2017 Long Term Incentive Plan [Member] \| Officer and Key Employees [Member]
Stock Option Plans [Line Items]
Shares available for grant	1,590,740	1,283,300	1,261,000
Stock options granted, exercise percentage, on the third anniversary date of the grant	34.00%	34.00%	34.00%
Stock options granted, exercise percentage, on the fourth anniversary date of the grant	33.00%	33.00%	33.00%
Stock options granted, exercise percentage, on the fifth anniversary date of the grant	33.00%	33.00%	33.00%

Stock Option Plans - Black-Scho

Stock Option Plans - Black-Scholes Option Pricing Model with Weighted Average (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected dividend yield	$ 2.1	$ 1.7	$ 2.3
Expected risk-free interest rate	0.70%	2.50%	2.70%
Volatility	17.30%	15.60%	15.10%
Expected life (in years)	5 years 4 months 24 days	5 years 6 months	5 years 6 months

Stock Option Plans - Stock Opti

Stock Option Plans - Stock Option Activity and Related Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Under Option, Beginning balance	7.9	8.8
Shares Under Option, Granted	1.6	1.3
Shares Under Option, Exercised	(1.8)	(1.9)
Shares Under Option, Forfeited or canceled	(0.2)	(0.3)
Shares Under Option, Ending balance	7.5	7.9
Shares Under Option, Exercisable at end of year	1.9	2
Shares Under Option, Ending unvested and expected to vest	5.3	5.7
Weighted Average Exercise Price, Beginning balance	$ 56.40	$ 50.16
Weighted Average Exercise Price, Granted	86.17	79.59
Weighted Average Exercise Price, Exercised	45.80	42.91
Weighted Average Exercise Price, Forfeited or canceled	65.87	57.33
Weighted Average Exercise Price, Ending balance	65.09	56.40
Weighted Average Exercise Price, Exercisable at end of year	47.17	45.03
Weighted Average Exercise Price, Ending unvested and expected to vest	$ 70.74	$ 59.76
Weighted Average Remaining Contractual Term (in years), Ending balance	3 years 10 months 9 days	3 years 9 months
Weighted Average Remaining Contractual Term (in years), Exercisable at end of year	1 year 9 months 29 days	1 year 9 months 25 days
Weighted Average Remaining Contractual Term (in years), Ending unvested and expected to vest	4 years 6 months 3 days	4 years 4 months 9 days
Aggregate Intrinsic Value, Ending Balance	$ 437.9	$ 308.6
Aggregate Intrinsic Value, Exercisable at end of year	147.2	101.9
Aggregate Intrinsic Value, Ending unvested and expected to vest	$ 278.1	$ 201.5

Stock Option Plans - Stock Op_2

Stock Option Plans - Stock Options Outstanding and Exercisable (Detail) - $ / shares shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	$ 43.71
Range of Exercise Prices, maximum	$ 86.17
Option Outstanding, Number Outstanding	7.5
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	3 years 10 months 9 days	3 years 9 months
Option Outstanding, Weighted Average Exercise Price	$ 65.09	$ 56.40	$ 50.16
Options Exercisable, Number Exercisable	1.9
Option Exercisable, Weighted Average Exercise Price	$ 47.17
Exercise Prices Range $ 43.71 - $ 43.71 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	43.71
Range of Exercise Prices, maximum	$ 43.71
Option Outstanding, Number Outstanding	1.4
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	2 years 2 months 15 days
Option Outstanding, Weighted Average Exercise Price	$ 43.71
Options Exercisable, Number Exercisable	0.7
Option Exercisable, Weighted Average Exercise Price	$ 43.71
Exercise Prices Range $ 46.17 - $ 46.87 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	46.17
Range of Exercise Prices, maximum	$ 46.87
Option Outstanding, Number Outstanding	0.9
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	11 months 19 days
Option Outstanding, Weighted Average Exercise Price	$ 46.33
Options Exercisable, Number Exercisable	0.9
Option Exercisable, Weighted Average Exercise Price	$ 46.33
Exercise Prices Range $ 49.55 - $ 56.86 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	49.55
Range of Exercise Prices, maximum	$ 56.86
Option Outstanding, Number Outstanding	1.3
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	3 years 2 months 15 days
Option Outstanding, Weighted Average Exercise Price	$ 56.83
Options Exercisable, Number Exercisable	0.3
Option Exercisable, Weighted Average Exercise Price	$ 56.81
Exercise Prices Range $ 70.74 - $ 70.74 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	70.74
Range of Exercise Prices, maximum	$ 70.74
Option Outstanding, Number Outstanding	1.1
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	4 years 2 months 15 days
Option Outstanding, Weighted Average Exercise Price	$ 70.74
Option Exercisable, Weighted Average Exercise Price	70.74
Exercise Prices Range $ 79.59 - $ 79.59 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	79.59
Range of Exercise Prices, maximum	$ 79.59
Option Outstanding, Number Outstanding	1.2
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	5 years 2 months 12 days
Option Outstanding, Weighted Average Exercise Price	$ 79.59
Option Exercisable, Weighted Average Exercise Price	79.59
Exercise Prices Range $ 86.17 - $ 86.17 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	86.17
Range of Exercise Prices, maximum	$ 86.17
Option Outstanding, Number Outstanding	1.6
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	6 years 2 months 12 days
Option Outstanding, Weighted Average Exercise Price	$ 86.17

Deferred Compensation - Additio

Deferred Compensation - Additional Information (Detail) - USD ($) shares in Millions	3 Months Ended					12 Months Ended
	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments And Employee Deferred Compensation Plan [Line Items]
Deferred Equity Participation Plan, distributions to key executives, age						age 62 (or the one-year anniversary of the date of the grant for participants over the age of 61 as of the grant date) or upon or after their actual retirement if later.
Deferred Equity Participation Sub-plans, distributions requisite service description						we annually make awards under sub-plans of the DEPP for certain production staff, which generally provide for vesting and/or distributions no sooner than five years from the date of awards, although certain awards vest and/or distribute after the earlier of fifteen years or the participant reaching age 65.
Deferred Equity Participation Sub-plans, distributions to key executives, age						age 65
Deferred Equity Participation Plan (DEPP) [Member]
Investments And Employee Deferred Compensation Plan [Line Items]
Awards approved by committee, value	$ 14,100,000			$ 10,100,000	$ 11,500,000
Charge to compensation expenses related to awards						$ 12,200,000	$ 9,800,000	$ 9,100,000
Unearned deferred compensation, value						$ 60,500,000	$ 64,500,000
Unearned deferred compensation, shares						2.6	2.9
Total intrinsic value of unvested equity based awards						$ 327,800,000	$ 276,300,000
Cash and equity awards with aggregate fair value vested and distributed to participants						41,200,000	3,100,000	6,400,000
Deferred Equity Participation Plan Sub Plans [Member]
Investments And Employee Deferred Compensation Plan [Line Items]
Awards approved by committee, value						1,800,000	2,600,000	900,000
Charge to compensation expenses related to awards						1,900,000	2,400,000	2,200,000
Distributions from the sub-plans						0	500,000	0
Deferred Cash Participation Plan (DCPP) [Member]
Investments And Employee Deferred Compensation Plan [Line Items]
Awards approved by committee, value	$ 3,000,000	$ 1,600,000	$ 7,700,000	$ 2,400,000	$ 5,600,000
Charge to compensation expenses related to awards						6,900,000	5,200,000	3,000,000
Cash and equity awards with aggregate fair value vested and distributed to participants						$ 3,200,000	$ 2,500,000	$ 3,600,000

Restricted Stock, Performance_3

Restricted Stock, Performance Share and Cash Awards - Additional Information (Detail)

Mar. 12, 2020USD ($)shares

Mar. 14, 2019USD ($)shares

Mar. 15, 2018USD ($)shares

Mar. 16, 2017USD ($)shares

Mar. 17, 2016USD ($)shares

Mar. 31, 2020shares

Mar. 31, 2019shares

Mar. 31, 2018shares

Dec. 31, 2020USD ($)TIMEshares

Dec. 31, 2019USD ($)shares

Dec. 31, 2018USD ($)shares

Dec. 31, 2017USD ($)shares

Mar. 31, 2017shares

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Share-based compensation, shares outstanding | shares

7,500,000

7,900,000

8,800,000

Officer and Key Employees [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Performance awards period, years

1 year

Restricted Stock Units (RSUs) [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Shares granted in the period | shares

405,870

399,900

420,200

422,610

414,700

439,100

Fair value of grants in period

$ 34,900,000

$ 31,800,000

$ 28,700,000

Share based payment award vesting date

Mar. 12,
2025

Mar. 14,
2024

Mar. 15,
2023

Period of service from grant date stock options awarded not subject to forfeiture

2 years

Restricted stock or unit expense

$ 40,000,000

29,800,000

27,200,000

Restricted Stock Units (RSUs) [Member] | Executive Officer [Member] | Minimum [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Minimum age of employee with not subject to award forfeiture on condition compliance

55 years

Unvested Restricted Stock [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Total intrinsic value

$ 302,400,000

215,100,000

Equity awards with an aggregate fair value

2,000,000

2,100,000

Performance Shares [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Equity awards with an aggregate fair value

$ 12,500,000

5,700,000

3,700,000

Shares authorized | shares

82,500

73,600

78,200

Performance share awards approved, Fair value

$ 7,100,000

$ 5,800,000

$ 5,300,000

Vesting period, years

2 years

2017 Performance Share Awards [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Provisional awards, terms

The 2020, 2019 and 2018 awards are subject to a three-year performance period that begins on January 1, 2020, 2019 and 2018, respectively, and vest on the three-year anniversary of the date of grant (March 12, 2023, March 14, 2022 and March 15, 2021).

Cash-based compensation awards, expenses

10,300,000

8,700,000

Performance awards expiration date

Jan. 1,
2020

Cash Awards [Member] | Officer and Key Employees [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Provisional awards, terms

The ultimate award value will be equal to the trailing twelve-month price of our common stock on December 31, 2022, multiplied by the number of units subject to the award, but limited to between 0.5 and 1.5 times the original value of the units determined as of the grant date.

Vesting period, years

3 years

Provisional compensation cash awards approved for future grant by compensation committee, value

$ 18,400,000

$ 16,500,000

$ 14,300,000

$ 17,400,000

Provisional compensation cash award approved for future grant by compensation committee, units | shares

213,000

206,800

255,000

397,000

200,000

242,000

209,000

385,000

Ultimate award value, multiples of original value of the units, minimum | TIME

0.5

Ultimate award value, multiples of original value of the units, maximum | TIME

1.5

Cash-based compensation awards, expenses

$ 0

2020 Provisional Cash Awards [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Cash-based compensation awards, expenses

$ 10,600,000

Performance awards expiration date

Jan. 1,
2023

2019 Provisional Cash Awards [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Cash-based compensation awards, expenses

Performance awards expiration date

Jan. 1,
2022

2019 Provisional Cash Awards [Member] | Officer and Key Employees [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Provisional compensation cash awards approved for future grant by compensation committee, value

$ 15,000,000

Provisional compensation cash award approved for future grant by compensation committee, units | shares

219,000

190,000

2018 Provisional Cash Awards [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Cash-based compensation awards, expenses

$ 9,900,000

$ 8,900,000

Performance awards expiration date

Jan. 1,
2021

2016 Provisional Cash Awards [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Provisional compensation cash award approved for future grant by compensation committee, units | shares

341,000

Cash-based compensation awards, expenses

$ 22,400,000

$ 11,700,000

Performance awards expiration date

Jan. 1,
2019

2015 Provisional Cash Awards [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Provisional compensation cash award approved for future grant by compensation committee, units | shares

269,000

Cash-based compensation awards, expenses

$ 15,800,000

2014 Provisional Cash Awards [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Provisional compensation cash award approved for future grant by compensation committee, units | shares

199,000

Cash-based compensation awards, expenses

$ 9,300,000

Long Term Incentive Plan [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Share-based compensation, shares outstanding, Value

$ 4,000,000

Share-based compensation, shares outstanding | shares

2,300,000

Shares granted in the period | shares

2,300,000

Long Term Incentive Plan [Member] | Minimum [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Period of service from grant date stock options awarded not subject to forfeiture

2 years

Long Term Incentive Plan [Member] | Executive Officer [Member] | Minimum [Member]

Common Stock Options Restricted Stock Warrants And Changes In Capitalization [Line Items]

Minimum age of employee with not subject to award forfeiture on condition compliance

55 years

Restricted Stock, Performance_4

Restricted Stock, Performance Share and Cash Awards - Schedule of Restricted Stock Awards Vesting Periods (Detail) - Restricted Stock Units Granted [Member] - shares	3 Months Ended			12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Vesting Period [Line Items]
Shares granted in the period	405,870	399,900	420,200	422,610	414,700	439,100
Vesting Period One Year [Member]
Vesting Period [Line Items]
Shares granted in the period				16,740	14,800	18,900
Vesting period, years				1 year
Vesting Period Two Years [Member]
Vesting Period [Line Items]
Shares granted in the period				8,870	12,000	12,700
Vesting period, years				2 years
Vesting Period Five Years [Member]
Vesting Period [Line Items]
Shares granted in the period				397,000	387,900	407,500
Vesting period, years				5 years

Retirement Plans - Reconciliati

Retirement Plans - Reconciliation of Balances of Pension Benefit Obligation and Fair Value of Plan Assets (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in pension benefit obligation:
Benefit obligation at beginning of year	$ 274,400,000	$ 253,200,000
Service cost	800,000	1,600,000	$ 800,000
Interest cost	8,000,000	9,800,000	9,300,000
Net actuarial loss	22,600,000	24,700,000
Benefits paid	(15,200,000)	(14,900,000)
Benefit obligation at end of year	290,600,000	274,400,000	253,200,000
Change in plan assets:
Fair value of plan assets at beginning of year	243,700,000	220,000,000
Actual return on plan assets	34,300,000	38,600,000
Contributions by the company	0	30,000,000	0
Benefits paid	(15,200,000)	(14,900,000)
Fair value of plan assets at end of year	262,800,000	243,700,000	$ 220,000,000
Funded status of the plan (underfunded)	(27,800,000)	(30,700,000)
Amounts recognized in the consolidated balance sheet consist of:
Noncurrent liabilities - accrued benefit liability	(27,800,000)	(30,700,000)
Accumulated other comprehensive loss - net actuarial loss	68,300,000	69,800,000
Net amount included in retained earnings	$ 40,500,000	$ 39,100,000

Retirement Plans - Components o

Retirement Plans - Components of Net Periodic Pension Benefit Cost and Other Changes in Plan Assets and Obligations Recognized in Earnings and Other Comprehensive Earnings (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net periodic pension cost:
Service cost	$ 0.8	$ 1.6	$ 0.8
Interest cost on benefit obligation	8	9.8	9.3
Expected return on plan assets	(16.4)	(14.8)	(16)
Amortization of net loss	6.2	7	4.9
Net periodic benefit cost	(1.4)	3.6	(1)
Other changes in plan assets and obligations recognized in other comprehensive earnings:
Net loss incurred	4.7	0.8	17.2
Amortization of net loss	(6.2)	(7)	(4.9)
Total recognized in other comprehensive loss	(1.5)	(6.2)	12.3
Total recognized in net periodic pension cost and other comprehensive loss	(2.9)	(2.6)	11.3
Estimated amortization for the following year:
Amortization of net loss	$ 5.8	$ 6.1	$ 7.2

Retirement Plans - Weighted Ave

Retirement Plans - Weighted Average Assumptions of Pension Benefit Obligation and Net Periodic Pension Benefit Cost (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Benefit Obligation [Abstract]
Discount rate, pension benefit obligation	2.25%	3.00%
Weighted average expected long-term rate of return on plan assets, pension benefit obligation	7.00%	7.00%
Discount rate, net periodic pension benefit cost	3.00%	4.00%	3.50%
Weighted average expected long-term rate of return on plan assets, net periodic pension benefit cost	7.00%	7.00%	7.00%

Retirement Plans - Schedule of

Retirement Plans - Schedule of Benefit Payments Expected to be Paid by Plan (Detail) $ in Millions	Dec. 31, 2019USD ($)
Defined Benefit Plan Estimated Future Benefit Payments [Abstract]
2021	$ 16.2
2022	16.5
2023	16.7
2024	16.7
2025	16.9
Years 2026 to 2030	$ 83.1

Retirement Plans - Summary of P

Retirement Plans - Summary of Plan's Weighted Average Asset Allocations (Detail)	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Total weighted average asset	100.00%	100.00%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total weighted average asset	63.00%	61.00%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total weighted average asset	30.00%	32.00%
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Total weighted average asset	7.00%	7.00%

Retirement Plans - Additional I

Retirement Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Expected period of return on plan assets, years	10 years	10 years
Minimum contribution by employer	$ 0	$ 0	$ 0
Discretionary contributions by employer	0	30,000,000	0
Fair value of plan assets	$ 262,800,000	243,700,000	220,000,000
Foreign Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching contributions by employer, percentage	100.00%
Percentage of eligible compensation for matching contributions by employer	5.00%
Contribution expense to plan	$ 44,300,000	39,800,000	34,900,000
Additional percentage of eligible compensation for matching contributions by employer	5.00%
Qualified Contributory Savings and Thrift 401(k) Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching contributions by employer, percentage	100.00%
Percentage of eligible compensation for matching contributions by employer	5.00%
Matching contributions vesting schedule	5 years
Contribution expense to plan	$ 63,600,000	59,400,000	53,900,000
Nonqualified Deferred Compensation Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of eligible compensation for matching contributions by employer	5.00%
Contribution expense to plan	$ 7,800,000	7,100,000	$ 6,500,000
Fair value of plan assets	$ 497,300,000	$ 452,900,000

Retirement Plans - Summary of_2

Retirement Plans - Summary of Plan's Assets Carried at Fair Value (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Total fair value	$ 262.8	$ 243.7	$ 220
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value	141.8	135.8
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value	$ 121	$ 107.9	$ 94.9

Retirement Plans - Reconcilia_2

Retirement Plans - Reconciliation of Beginning and Ending Balances for Level 3 Assets of Plan Measured at Fair Value (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	$ 243.7	$ 220
Fair value of plan assets at end of year	262.8	243.7
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	107.9	94.9
Settlements	(2.7)
Unrealized gain	15.8	13
Fair value of plan assets at end of year	$ 121	$ 107.9

Investments - Investments Repor

Investments - Investments Reported in Other Current and Non-Current Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Assets	$ 22.4	$ 40
Funding commitments	0.9
Chem-Mod LLC [Member]
Schedule of Equity Method Investments [Line Items]
Assets	4	4
Chem-Mod International LLC [Member]
Schedule of Equity Method Investments [Line Items]
Assets	2	2
Clean-Coal Investments [Member] \| Controlling Interest [Member] \| Twenty 2011 Era Clean Coal Plants [Member]
Schedule of Equity Method Investments [Line Items]
Assets	12.4	29.2
Funding commitments	0.9
Clean-Coal Investments [Member] \| Noncontrolling Interests [Member] \| One 2011 Era Clean Coal Plant [Member]
Schedule of Equity Method Investments [Line Items]
Assets	0.1	0.3
Other Investments [Member]
Schedule of Equity Method Investments [Line Items]
Assets	$ 3.9	$ 4.5

Investments - Investments Rep_2

Investments - Investments Reported in Other Current and Non-Current Assets (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2020Plant
Fourteen 2009 Era Clean Coal Plants [Member] \| Controlling Interest [Member]
Schedule of Equity Method Investments [Line Items]
Number of coal plants	14
One 2011 Era Clean Coal Plant [Member] \| Noncontrolling Interests [Member]
Schedule of Equity Method Investments [Line Items]
Number of coal plants	1
Twenty 2011 Era Clean Coal Plants [Member] \| Controlling Interest [Member]
Schedule of Equity Method Investments [Line Items]
Number of coal plants	20

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Ownership interest held	50.00%
Total assets of variable interest entities	$ 22,331.4	$ 19,634.8	$ 16,334
Total liabilities of variable interest entities	$ 16,098.7	14,419.3
Ownership interest held	50.00%
Variable Interest Entity, Not Primary Beneficiary [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest held	12.00%
Chem-Mod Clean-Coal Venture - U.S. and Canadian Operations [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest held	46.50%
Chem-Mod Clean-Coal Venture [Member]
Schedule of Equity Method Investments [Line Items]
Total revenues of limited liability companies	$ 74.3	81.9
Total expenses of limited liability companies	10.6	17.5
Chem-Mod Clean-Coal Venture [Member] \| VIE [Member]
Schedule of Equity Method Investments [Line Items]
Total assets of variable interest entities	19	16.3
Total liabilities of variable interest entities	$ 4.4	$ 2.8
Chem-Mod International LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest held	31.50%

Investments - Clean Coal Invest

Investments - Clean Coal Investments - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)EntityPlant
Chem-Mod LLC [Member]
Schedule of Equity Method Investments [Line Items]
Number of clean coal production plants owned \| Plant	35
Chem-Mod LLC [Member] \| 2009 Era Plants [Member]
Schedule of Equity Method Investments [Line Items]
Number of clean coal production plants owned \| Plant	14
Chem-Mod LLC [Member] \| 2011 Era Plants [Member]
Schedule of Equity Method Investments [Line Items]
Number of clean coal production plants owned \| Plant	21
Clean-Coal Investments [Member]
Schedule of Equity Method Investments [Line Items]
Number of variable interest entities \| Entity	1
Clean-Coal Investments [Member] \| VIE [Member]
Schedule of Equity Method Investments [Line Items]
Total assets of limited liability companies	$ 36.6
Total liability of limited liability companies	36
Total revenues of limited liability companies	35.2
Total expenses of limited liability companies	$ 43.9

Investments - Other Investments

Investments - Other Investments - Additional Information (Detail)	Dec. 31, 2020USD ($)VentureInvestment	Dec. 31, 2019USD ($)
Schedule of Equity Method Investments [Line Items]
Assets	$ 22,400,000	$ 40,000,000
Non controlling interest certified low-income housing developments \| Investment	8
Liabilities	$ 16,098,700,000	14,419,300,000
Other Investments [Member]
Schedule of Equity Method Investments [Line Items]
Assets	3,900,000	$ 4,500,000
Other Investments [Member] \| Variable Interest Entity, Not Primary Beneficiary [Member]
Schedule of Equity Method Investments [Line Items]
Assets	4,800,000
Liabilities	$ 500,000
Other Investments [Member] \| Four Venture Capital Funds [Member]
Schedule of Equity Method Investments [Line Items]
Non controlling interest in venture capital funds number \| Venture	4
Assets	$ 3,900,000
Other Investments [Member] \| Eight Certified Low Income Housing Developments [Member] \| Variable Interest Entity, Not Primary Beneficiary [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value of investments	$ 0

Leases - Components of Lease Ex

Leases - Components of Lease Expense (Detail) $ in Millions	12 Months Ended
Leases - Components of Lease Expense (Detail) $ in Millions	Dec. 31, 2020USD ($)
Total net lease expense	$ 147.4
Operating [Member]
Operating lease expense	126.5
Variable lease expense	22
Investment Income [Member]
Sublease income	$ (1.1)

Leases - Summary of Supplementa

Leases - Summary of Supplemental Cash Flow Information Related to Leases (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 120.1
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 71.2

Leases - Summary of Supplemen_2

Leases - Summary of Supplemental Balance Sheet Information Related to Leases (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Leases [Abstract]
Lease right-of-use assets	$ 373.9	$ 393.5	$ 379.6
Other current lease liabilities	$ 88.8
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	ajg:AccruedCompensationAndOtherAccruedLiabilities
Lease liabilities	$ 320.9	$ 340.9
Total lease liabilities	$ 409.7		$ 420.3
Weighted-average remaining lease term, years	5 years 3 months 18 days
Weighted-average discount rate	3.60%

Leases - Maturities of Operatin

Leases - Maturities of Operating Lease Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Jan. 01, 2019
Leases [Abstract]
2021	$ 108.5
2022	93.9
2023	75.1
2024	54.8
2025	41.6
Thereafter	77.8
Total lease payments	451.7
Less interest	(42)
Operating lease liabilities	$ 409.7	$ 420.3

Leases - Additional Information

Leases - Additional Information (Detail) $ in Millions	12 Months Ended
Leases - Additional Information (Detail) $ in Millions	Dec. 31, 2020USD ($)
Lessee, operating lease, option to extend	5.0 years
Operating lease liability not yet commenced	$ 0.3
Minimum [Member]
Operating lease, remaining lease term	1 month 6 days
Lessee, operating lease, lease not yet commenced, term of contract	6 months
Maximum [Member]
Operating lease, remaining lease term	11 years 8 months 12 days
Lessee, operating lease, lease not yet commenced, term of contract	5 years 4 months 24 days

Derivatives and Hedging Activ_3

Derivatives and Hedging Activity - Summary of Notional and Fair Values of Derivative Instruments (Detail) - USD ($)		Dec. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Notional Amount		$ 598,600,000	$ 831,700,000
Derivative Assets		13,700,000	21,200,000
Derivative Liabilities		69,300,000	52,400,000
Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional Amount		550,000,000	800,000,000
Interest Rate Contracts [Member] \| Other current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets			2,800,000
Interest Rate Contracts [Member] \| Other noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets			5,400,000
Interest Rate Contracts [Member] \| Accrued compensation and other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities		54,500,000	25,000,000
Interest Rate Contracts [Member] \| Other noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities		10,900,000	23,000,000
Foreign Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	[1]	48,600,000	31,700,000
Foreign Exchange Contracts [Member] \| Other current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets	[1]	5,900,000	4,500,000
Foreign Exchange Contracts [Member] \| Other noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets	[1]	7,800,000	8,500,000
Foreign Exchange Contracts [Member] \| Accrued compensation and other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	[1]	600,000	1,800,000
Foreign Exchange Contracts [Member] \| Other noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	[1]	$ 3,300,000	$ 2,600,000

[1]	Included within foreign exchange contracts at December 31, 2020 were $354.7 million of call options offset with $354.7 million of put options, and $9.0 million of buy forwards offset with $57.6 million of sell forwards.

Derivatives and Hedging Activ_4

Derivatives and Hedging Activity - Summary of Notional and Fair Values of Derivative Instruments (Parenthetical) (Detail) - Foreign Exchange Contracts [Member] - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Call Options [Member]
Derivatives, Fair Value [Line Items]
Foreign exchange derivative contracts	$ 354.7	$ 342
Put Options [Member]
Derivatives, Fair Value [Line Items]
Foreign exchange derivative contracts	354.7	342
Forward Contracts [Member] \| Call Options [Member]
Derivatives, Fair Value [Line Items]
Foreign exchange derivative contracts	57.6	43.8
Forward Contracts [Member] \| Put Options [Member]
Derivatives, Fair Value [Line Items]
Foreign exchange derivative contracts	$ 9	$ 12.1

Derivatives and Hedging Activ_5

Derivatives and Hedging Activity - Summary of Amounts of Derivative Gains (Losses) Recognized In Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss	[1]	$ (97.1)	$ (37.1)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Earnings		(6.3)	(5.2)
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing		2.3	1.3
Interest expense [Member] \| Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss	[1]	(92.5)	(47)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Earnings		(1.1)	(1.2)
Commission revenue [Member] \| Foreign Exchange Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Loss	[1]	(4.6)	9.9
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Earnings		(2.4)	(1.6)
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing		(0.4)	(0.8)
Compensation expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Earnings		(1.6)	(1.4)
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing		1.6	1.2
Operating expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Earnings		(1.2)	(1)
Amount of Gain (Loss) Recognized in Earnings Related to Amount Excluded from Effectiveness Testing		$ 1.1	$ 0.9

[1]	During 2020, the amount excluded from the assessment of hedge effectiveness for our foreign exchange contracts recognized in accumulated other comprehensive loss was a loss of $1.3 million.

Derivatives and Hedging Activ_6

Derivatives and Hedging Activity - Summary of Amounts of Derivative Gains (Losses) Recognized In Accumulated Other Comprehensive Loss (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Other comprehensive income (loss), foreign currency transaction and translation adjustment, net of tax	$ 184.1	$ 44.5	$ (199.7)
Foreign Exchange [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Other comprehensive income (loss), foreign currency transaction and translation adjustment, net of tax	$ (1.3)

Derivatives and Hedging Activ_7

Derivatives and Hedging Activity - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)
Scenario, Forecast [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Estimated pretax loss to be reclassified from accumulated other comprehensive loss into earnings	$ 2.5

Commitments, Contingencies an_3

Commitments, Contingencies and Off-Balance Sheet Arrangements - Contractual Obligations (Detail) $ in Millions	Dec. 31, 2020USD ($)
Note Purchase Agreements [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2021	$ 75
Contractual Obligations, Payments Due by Period, 2022	200
Contractual Obligations, Payments Due by Period, 2023	250
Contractual Obligations, Payments Due by Period, 2024	475
Contractual Obligations, Payments Due by Period, 2025	200
Contractual Obligations, Payments Due by Period, Thereafter	3,148
Contractual Obligations, Payments Due by Period, Total	4,348
Premium Financing Debt Facility [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2021	203.6
Contractual Obligations, Payments Due by Period, Total	203.6
Interest On Debt [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2021	189.5
Contractual Obligations, Payments Due by Period, 2022	183.6
Contractual Obligations, Payments Due by Period, 2023	174.7
Contractual Obligations, Payments Due by Period, 2024	158
Contractual Obligations, Payments Due by Period, 2025	143.4
Contractual Obligations, Payments Due by Period, Thereafter	601.9
Contractual Obligations, Payments Due by Period, Total	1,451.1
Total Debt Obligations [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2021	468.1
Contractual Obligations, Payments Due by Period, 2022	383.6
Contractual Obligations, Payments Due by Period, 2023	424.7
Contractual Obligations, Payments Due by Period, 2024	633
Contractual Obligations, Payments Due by Period, 2025	343.4
Contractual Obligations, Payments Due by Period, Thereafter	3,749.9
Contractual Obligations, Payments Due by Period, Total	6,002.7
Operating Lease Obligations [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2021	108.5
Contractual Obligations, Payments Due by Period, 2022	93.9
Contractual Obligations, Payments Due by Period, 2023	75.1
Contractual Obligations, Payments Due by Period, 2024	54.8
Contractual Obligations, Payments Due by Period, 2025	41.6
Contractual Obligations, Payments Due by Period, Thereafter	77.8
Contractual Obligations, Payments Due by Period, Total	451.7
Less Sublease Arrangements [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Receivable by Period, 2021	(0.3)
Contractual Obligations, Payments Receivable by Period, 2022	(0.3)
Contractual Obligations, Payments Receivable by Period, 2023	(0.2)
Contractual Obligations, Payments Receivable by Period, 2024	(0.2)
Contractual Obligations, Payments Receivable by Period, 2025	(0.2)
Contractual Obligations, Payments Receivable by Period, Thereafter	(0.5)
Contractual Obligations, Payments Receivable by Period, Total	(1.7)
Outstanding Purchase Obligations [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2021	75.3
Contractual Obligations, Payments Due by Period, 2022	49.4
Contractual Obligations, Payments Due by Period, 2023	30.8
Contractual Obligations, Payments Due by Period, 2024	21.9
Contractual Obligations, Payments Due by Period, 2025	16.7
Contractual Obligations, Payments Due by Period, Thereafter	22.7
Contractual Obligations, Payments Due by Period, Total	216.8
Total Contractual Obligations [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Contractual Obligations, Payments Due by Period, 2021	651.6
Contractual Obligations, Payments Due by Period, 2022	526.6
Contractual Obligations, Payments Due by Period, 2023	530.4
Contractual Obligations, Payments Due by Period, 2024	709.5
Contractual Obligations, Payments Due by Period, 2025	401.5
Contractual Obligations, Payments Due by Period, Thereafter	3,849.9
Contractual Obligations, Payments Due by Period, Total	$ 6,669.5

Commitments, Contingencies an_4

Commitments, Contingencies and Off-Balance Sheet Arrangements - Additional Information (Detail)	Dec. 23, 2020USD ($)	Dec. 31, 2020USD ($)ft²EmployeeEntityLetterOfCreditCompany	Dec. 31, 2019USD ($)Entity	Dec. 31, 2018USD ($)Entity	Dec. 31, 2020USD ($)ft²EntityLetterOfCredit
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Accrued Liability		$ 50,000,000			$ 50,000,000
Cash Paid		$ 398,300,000
Number of square feet \| ft²		360,000			360,000
Number of employees will accommodate at new facility \| Employee		2,000
Total rent expense		$ 154,000,000	$ 148,100,000	$ 140,000,000
Number of companies acquired \| Entity		135	116	112	583
Aggregate amount of maximum earnout obligations related to acquisitions		$ 1,128,100,000	$ 982,900,000
Aggregate amount of maximum earnout obligations related to acquisitions, recorded in consolidated balance sheet		592,200,000	$ 565,000,000
Aggregate amount of earnout obligation expected settlement in cash or stock at option		493,700,000			$ 493,700,000
Aggregate amount of earnout obligation expected settlement in cash		$ 98,500,000			$ 98,500,000
Ownership interest		50.00%			50.00%
Debt		$ 19,600,000			$ 19,600,000
Liabilities recorded on self-insurance		17,500,000			$ 17,500,000
Income tax credits and adjustments		$ 108,000,000
Security Deposit [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Number of letters of credit issued \| LetterOfCredit		1			1
Collateral [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Number of letters of credit issued \| LetterOfCredit		1			1
Self-Insurance Deductibles [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Number of letters of credit issued \| LetterOfCredit		2			2
Rent-A-Captive Facility [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Number of letters of credit issued \| LetterOfCredit		7			7
Errors And Omissions [Member] \| Up to $4.5 Million [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Insurance claims, amount retained		$ 4,500,000
Errors And Omissions [Member] \| Up to $10 Million [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Insurance claims, amount retained		10,000,000
Insurance claim arise during ordinary course of business		10,000,000			$ 10,000,000
Errors And Omissions [Member] \| Up to $20.0 Million [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Insurance claims, amount retained		20,000,000
Errors And Omissions [Member] \| Up to $27.0 Million [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Insurance claims, amount retained		27,000,000
Letter of Credit [Member] \| Security Deposit [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt		500,000			500,000
Letter of Credit [Member] \| Collateral [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt		1,000,000			1,000,000
Letter of Credit [Member] \| Self-Insurance Deductibles [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt		9,400,000			9,400,000
Liabilities recorded on self-insurance		17,500,000			17,500,000
Letter of Credit [Member] \| Rent-A-Captive Facility [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Debt		$ 7,500,000			7,500,000
Minimum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Number of micro-captive insurance companies organized or managed \| Company		100
Minimum [Member] \| Errors And Omissions [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Actuarial range value		$ 2,600,000			2,600,000
Minimum [Member] \| Errors And Omissions [Member] \| Up to $4.5 Million [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Insurance claim arise during ordinary course of business		10,000,000			10,000,000
Minimum [Member] \| Errors And Omissions [Member] \| Up to $20.0 Million [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Insurance claim arise during ordinary course of business		100,000,000			100,000,000
Minimum [Member] \| Errors And Omissions [Member] \| Up to $27.0 Million [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Insurance claim arise during ordinary course of business		$ 240,000,000			$ 240,000,000
Minimum [Member] \| Unconsolidated Investments in Enterprises [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Ownership interest		1.00%			1.00%
Maximum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Ownership interest		50.00%			50.00%
Maximum [Member] \| Errors And Omissions [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Actuarial range value		$ 6,400,000			$ 6,400,000
Maximum [Member] \| Errors And Omissions [Member] \| Up to $4.5 Million [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Insurance claim arise during ordinary course of business		100,000,000			100,000,000
Maximum [Member] \| Errors And Omissions [Member] \| Up to $20.0 Million [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Insurance claim arise during ordinary course of business		240,000,000			240,000,000
Maximum [Member] \| Errors And Omissions [Member] \| Up to $27.0 Million [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Insurance claim arise during ordinary course of business		$ 350,000,000			$ 350,000,000
Maximum [Member] \| Unconsolidated Investments in Enterprises [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Ownership interest		50.00%			50.00%
Tax Increment Financing [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Property tax credits receivable period		15 years
Economic development for growing economy tax credit		$ 25,500,000			$ 25,500,000
Tax Increment Financing [Member] \| Minimum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Property tax credit expect to receive		60,000,000			60,000,000
Tax Increment Financing [Member] \| Maximum [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Property tax credit expect to receive		90,000,000			90,000,000
Ashton Tiffany, LLC (AT) [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Accrued Liability		48,200,000			48,200,000
Cash Paid		48,300,000
Ashton Tiffany, LLC (AT) [Member] \| Common Stock [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Accrued Liability		$ 48,200,000			$ 48,200,000
The Bollington Wilson Group [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Percentage of equity interests acquired	100.00%
Cash Paid	$ 330,000,000

Commitments, Contingencies an_5

Commitments, Contingencies and Off-Balance Sheet Arrangements - Off-Balance Sheet Commitments (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Amount of Commitment Expiration by Period - 2021	$ 0.2
Amount of Commitment Expiration by Period - 2022	0.2
Amount of Commitment Expiration by Period - 2023	0.2
Amount of Commitment Expiration by Period - 2024	0.2
Amount of Commitment Expiration by Period - 2025	0.2
Amount of Commitment Expiration by Period - Thereafter	18.6
Total Amounts Committed	19.6
Financial Guarantees [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Amount of Commitment Expiration by Period - 2021	0.2
Amount of Commitment Expiration by Period - 2022	0.2
Amount of Commitment Expiration by Period - 2023	0.2
Amount of Commitment Expiration by Period - 2024	0.2
Amount of Commitment Expiration by Period - 2025	0.2
Amount of Commitment Expiration by Period - Thereafter	0.2
Total Amounts Committed	1.2
Letters of Credit [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Amount of Commitment Expiration by Period - Thereafter	18.4
Total Amounts Committed	$ 18.4

Commitments, Contingencies an_6

Commitments, Contingencies and Off-Balance Sheet Arrangements - Outstanding Letters of Credit, Financial Guarantees and Funding Commitments (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Maximum Exposure	$ 19.6
Liability Recorded	$ 17.5
Credit Support Under Letters of Credit for Deductibles Due by Us on Our Own Insurance Coverage's Expires After 2025 [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Collateral	None
Compensation to Us	None
Maximum Exposure	$ 9.4
Liability Recorded	$ 17.5
Credit Enhancement Under Letters of Credit for Our Captive Insurance Operations to Meet Minimum Statutory Capital Requirement's Expires After 2025 [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Collateral	None
Compensation to Us	Reimbursement of LOC fees
Maximum Exposure	$ 7.5
Collateral Related to Claims Funds Held in a Fiduciary Capacity by a Recent Acquisition Expires 2021 [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Collateral	None
Compensation to Us	None
Maximum Exposure	$ 1
Credit Support Under Letters of Credit in Lieu of Security Deposit for Acquisition Lease Expires 2025 [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Collateral	None
Compensation to Us	None
Maximum Exposure	$ 0.5
Financial Guarantees of Loans to Five Canadian Based Employees Trigger [Member]
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items]
Collateral	(1)
Compensation to Us	None
Maximum Exposure	$ 1.2

Insurance Operations - Summary

Insurance Operations - Summary of Reconciliations of Direct to Net premiums on Written and Earned Basis Related to Wholly Owned Underwriting Enterprise Subsidiary (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Premiums Written And Earned [Abstract]
Written, Direct	$ 37.7	$ 44.6	$ 57.6
Written, Assumed	0.1	1	4.7
Written, Ceded	(37.8)	(45.6)	(62.3)
Earned, Direct	40.7	59.1	53.2
Earned, Assumed	0.9	1.9	4.6
Earned, Ceded	$ (41.6)	$ (61)	$ (57.8)

Insurance Operations - Addition

Insurance Operations - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Insurance [Abstract]
Reinsurance recoverables amount	$ 48.5	$ 45.7

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Expense Benefit [Line Items]
Interest expense, domestic deposits	$ 24	$ 40.1	$ 65.8
Net unrecognized tax benefits	9.5	9.4
Accrued interest and penalties related to unrecognized tax benefits	$ 3	3.1
Open tax year	2011 2012
Deferred tax liabilities	$ 495.1	490.8
Net operating loss carryforwards	$ 36.1	37.2
Net operating loss carryforward expiration year	2023
Undistributed earnings of foreign subsidiaries	$ 658.9	574
Deferred income taxes	1,085.8	945.6
Deferred tax assets included due to deferral of payroll taxes	12.9
State Tax Credits [Member]
Income Tax Expense Benefit [Line Items]
Deferred tax credits	$ 15
Deferred tax credits expiration year	2025
HR One [Member]
Income Tax Expense Benefit [Line Items]
Deferred income taxes			$ 2.9
General Business and Other Tax Credits [Member]
Income Tax Expense Benefit [Line Items]
Deferred tax credits	$ 983
Deferred tax credits expiration year	2034
Noncurrent Liabilities [Member]
Income Tax Expense Benefit [Line Items]
Deferred tax liabilities	$ 106.9	$ 127.5

Income Taxes - Components of Ea

Income Taxes - Components of Earnings Before Income Taxes and Provision for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
United States	$ 524.4	$ 388.4	$ 337.6
Foreign, principally Australia, Canada, New Zealand and the U.K.	346.5	237.7	141.8
Earnings before income taxes	870.9	626.1	479.4
Federal Current	43.6	3.8
Federal Deferred	(112.4)	(142.5)	(214)
Total Provision (benefit) for income taxes, Federal	(68.8)	(138.7)	(214)
State and local Current	36.6	11.1	15.4
State and local Deferred	(19.3)	(6)	(29)
Total Provision (benefit) for income taxes, State and local	17.3	5.1	(13.6)
Foreign Current	94.6	66.6	60.7
Foreign Deferred	(30.3)	(22.7)	(29.6)
Total Provision (benefit) for income taxes, Foreign	64.3	43.9	31.1
Total provision (benefit) for income taxes	$ 12.8	$ (89.7)	$ (196.5)

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Provision for Income Taxes with Federal Statutory Income Tax Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal statutory rate	$ 182.9	$ 131.5	$ 100.7
State income taxes - net of Federal benefit	22.2	4.4	8.5
Differences related to non U.S. operations	(2.5)	(10.1)	(14.8)
Alternative energy and other tax credits	(154.3)	(196.1)	(252.9)
Other permanent differences	(15.7)	(7.6)	0.9
U.S. repatriation tax			(1.8)
Stock-based compensation	(31.4)	(16.2)	(15)
Changes in unrecognized tax benefits		0.8	(0.2)
Change in valuation allowance	6.5	7.5	(22)
Change in U.S. and U.K. tax rates	5.5	(3.7)
Other	(0.4)	(0.2)	0.1
Total provision (benefit) for income taxes	$ 12.8	$ (89.7)	$ (196.5)
Federal statutory rate, % of Pretax Earnings	21.00%	21.00%	21.00%
State income taxes-net of Federal benefit, % of Pretax Earnings	2.60%	0.70%	1.80%
Differences related to non U.S. operations, % of Pretax Earnings	(0.30%)	(1.60%)	(3.10%)
Alternative energy and other tax credits, % of Pretax Earnings	(17.70%)	(31.30%)	(52.80%)
Other permanent differences, % of Pretax Earnings	(1.80%)	(1.20%)	0.20%
U.S. repatriation tax			(0.40%)
Stock-based compensation	(3.60%)	(2.60%)	(3.10%)
Changes in unrecognized tax benefits, % of Pretax Earnings		0.10%
Change in valuation allowance, % of Pretax Earnings	0.70%	1.20%	(4.60%)
Change in U.S. and U.K. tax rates	0.60%	(0.60%)
Total provision (benefit) for income taxes, % of Pretax Earnings	1.50%	(14.30%)	(41.00%)

Income Taxes - Gross Unrecogniz

Income Taxes - Gross Unrecognized Tax Benefit (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Gross unrecognized tax benefits at January	$ 11.5	$ 10.7
Increases in tax positions for current year	2.9	2.1
Settlements	(1.1)	(0.4)
Lapse in statute of limitations	(1.2)	(1.1)
Increases in tax positions for prior years	0.2	0.6
Decreases in tax positions for prior years	(1.1)	(0.4)
Gross unrecognized tax benefits at December	$ 11.2	$ 11.5

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Alternative minimum tax and other credit carryforwards	$ 998	$ 962.1
Accrued and unfunded compensation and employee benefits	239.9	156
Amortizable intangible assets	61.3	54.3
Compensation expense related to stock options	14.4	11.3
Accrued liabilities	65.7	63.9
Accrued pension liability	9.3	9.9
Investments	1.3	0.9
Net operating loss carryforwards	36.1	37.2
Capital loss carryforwards	9	12.6
Lease liabilities	96.3	65.3
Hedging instruments	34.6	11.7
Other	2.8	4.3
Total deferred tax assets	1,568.7	1,389.5
Valuation allowance for deferred tax assets	(94.9)	(80.5)
Deferred tax assets	1,473.8	1,309
Nondeductible amortizable intangible assets	316.9	322.4
Investment-related partnerships	8.5	9.1
Depreciable fixed assets	32.4	22.4
Right-of-use assets	92.2	62.6
Revenue recognition	33.1	63.7
Other prepaid items	12	10.6
Total deferred tax liabilities	495.1	490.8
Net deferred tax assets	$ 978.7	$ 818.2

Supplemental Disclosures of C_3

Supplemental Disclosures of Cash Flow Information - Cash Flow (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash And Cash Equivalents [Abstract]
Interest paid	$ 188.9	$ 169.2	$ 139.2
Income taxes paid, net	$ 113	$ 22.2	$ 68.1

Supplemental Disclosures of C_4

Supplemental Disclosures of Cash Flow Information - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
AMT credit and other U.S. federal refunds	$ (28.5)	$ (63.6)	$ (2.4)
Qualified Contributory Savings and Thrift 401(k) Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching contributions by employer, percentage	100.00%
Percentage of eligible compensation for matching contributions by employer	5.00%
Matching contributions vesting schedule	5 years
Contribution expense to plan	$ 63.6	$ 59.4	$ 53.9

Supplemental Disclosures of C_5

Supplemental Disclosures of Cash Flow Information - Cash Equivalents And Restricted Cash (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 664.6	$ 604.8	$ 607.2
Restricted cash	2,909.7	2,019.1	1,629.6
Total cash, cash equivalents and restricted cash	$ 3,574.3	$ 2,623.9	$ 2,236.8

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Earnings - Schedule of Accumulated Other Comprehensive Earnings (Loss) Attributable to Controlling Interests (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ (759.6)
Ending Balance	(643.6)	$ (759.6)
Pension Liability [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(56.5)	(61.2)	$ (43)
Reclassification to retained earnings of income tax effects related to the TCJA			(7.9)
Net change in period	0.4	4.7	(10.3)
Ending Balance	(56.1)	(56.5)	(61.2)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(674.8)	(719)	(521.3)
Net change in period	183.7	44.2	(197.7)
Ending Balance	(491.1)	(674.8)	(719)
Fair Value of Derivative Investments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(28.3)	(5.4)	8.9
Reclassification to retained earnings of income tax effects related to the TCJA			1.3
Net change in period	(68.1)	(22.7)	(15.6)
Ending Balance	(96.4)	(28.3)	(5.4)
Fair Value of Derivative Investments [Member] \| Cumulative Effect Period Of Adoption Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance		(0.2)
Ending Balance			(0.2)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(759.6)	(785.6)	(555.4)
Reclassification to retained earnings of income tax effects related to the TCJA			(6.6)
Net change in period	116	26.2	(223.6)
Ending Balance	$ (643.6)	(759.6)	(785.6)
Accumulated Other Comprehensive Loss [Member] \| Cumulative Effect Period Of Adoption Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance		$ (0.2)
Ending Balance			$ (0.2)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Earnings - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Expense related to pension liability reclassified from accumulated other comprehensive earnings	$ 6,100,000	$ 7,000,000	$ 4,900,000
Income (expense) related to fair value of derivative investments reclassified from accumulated other comprehensive earnings	6,300,000	5,200,000	5,700,000
Foreign currency translation reclassified from accumulated other comprehensive earnings	$ 0	$ 0	$ 0

Quarterly Operating Results (_3

Quarterly Operating Results (unaudited) - Quarterly Operating Results (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Total revenues	$ 1,703.6	$ 1,849.1	$ 1,584	$ 1,866.9	$ 1,721.4	$ 1,825.2	$ 1,657.8	$ 1,990.6	$ 7,003.6	$ 7,195	$ 6,934
Total expenses	1,569.9	1,639.6	1,412.3	1,510.9	1,637.4	1,710.4	1,552.3	1,668.8	6,132.7	6,568.9	6,454.6
Earnings before income taxes	133.7	209.5	171.7	356	84	114.8	105.5	321.8	870.9	626.1	479.4
Net earnings attributable to controlling interests	$ 142.2	$ 176.6	$ 153.7	$ 346.3	$ 98.5	$ 126.1	$ 110.1	$ 334.1	$ 818.8	$ 668.8	$ 633.5
Basic net earnings per share	$ 0.74	$ 0.92	$ 0.81	$ 1.83	$ 0.53	$ 0.68	$ 0.59	$ 1.81	$ 4.29	$ 3.60	$ 3.47
Diluted net earnings per share	$ 0.72	$ 0.90	$ 0.79	$ 1.79	$ 0.51	$ 0.66	$ 0.58	$ 1.77	$ 4.20	$ 3.52	$ 3.40

Segment Information - Additiona

Segment Information - Additional Information (Detail)	12 Months Ended
Segment Information - Additional Information (Detail)	Dec. 31, 2020Segment
Segment Reporting [Abstract]
Number of reportable segments	3

Segment Information - Schedule

Segment Information - Schedule of Segment Reporting Information by Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenues before reimbursements									$ 6,851.9	$ 7,056.4	$ 6,792.4
Reimbursements									151.7	138.6	141.6
Total revenues	$ 1,703.6	$ 1,849.1	$ 1,584	$ 1,866.9	$ 1,721.4	$ 1,825.2	$ 1,657.8	$ 1,990.6	7,003.6	7,195	6,934
Compensation									3,466.5	3,339.5	3,026.3
Operating									906.5	1,068.5	903.7
Reimbursements									151.7	138.6	141.6
Cost of revenues from clean coal activities									882.1	1,352.8	1,816
Interest									196.4	179.8	138.4
Depreciation									145.1	140.4	127.8
Amortization									417.3	334	291.2
Change in estimated acquisition earnout payables									(32.9)	15.3	9.6
Total expenses	1,569.9	1,639.6	1,412.3	1,510.9	1,637.4	1,710.4	1,552.3	1,668.8	6,132.7	6,568.9	6,454.6
Earnings (loss) before income taxes	133.7	209.5	171.7	356	84	114.8	105.5	321.8	870.9	626.1	479.4
Provision (benefit) for income taxes									12.8	(89.7)	(196.5)
Net earnings (loss)									858.1	715.8	675.9
Net earnings attributable to noncontrolling interests									39.3	47	42.4
Net earnings (loss) attributable to controlling interests	142.2	$ 176.6	$ 153.7	$ 346.3	98.5	$ 126.1	$ 110.1	$ 334.1	818.8	668.8	633.5
Net foreign exchange (loss) gain									(2.9)	(6.7)	2.9
Total identifiable assets	22,331.4				19,634.8				22,331.4	19,634.8	16,334
Goodwill - net	6,127				5,618.5				6,127	5,618.5	4,625.6
Amortizable intangible assets - net	2,399.9				2,318.7				2,399.9	2,318.7	1,773
Unites States [Member]
Segment Reporting Information [Line Items]
Total revenues									5,048.9	5,379.1	5,377.8
Total identifiable assets	11,786.3				10,782.7				11,786.3	10,782.7	9,237.6
Goodwill - net	3,433				3,196.9				3,433	3,196.9
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total revenues									1,034.4	963.4	773.9
Total identifiable assets	6,274.3				5,091.1				6,274.3	5,091.1	3,862.3
Goodwill - net	1,343.4				1,190.7				1,343.4	1,190.7
Australia [Member]
Segment Reporting Information [Line Items]
Total revenues									314.5	298.6	290.6
Total identifiable assets	1,462.9				1,307.9				1,462.9	1,307.9	1,143.3
Goodwill - net	473.6				427				473.6	427
Canada [Member]
Segment Reporting Information [Line Items]
Total revenues									249.1	226	185.4
Total identifiable assets	1,058.4				916.7				1,058.4	916.7	787.5
Goodwill - net	492.9				454.4				492.9	454.4
New Zealand [Member]
Segment Reporting Information [Line Items]
Total revenues									154.4	160.8	157.5
Total identifiable assets	790.1				718.7				790.1	718.7	709.8
Goodwill - net	232.6				218.1				232.6	218.1
Other Foreign [Member]
Segment Reporting Information [Line Items]
Total revenues									202.3	167.1	148.8
Total identifiable assets	959.4				817.7				959.4	817.7	593.5
Goodwill - net	151.5				131.4				151.5	131.4
Commissions [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									3,591.9	3,320.6	2,920.7
Broker Fees [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									1,957.9	1,911.1	1,756.3
Supplemental Revenue [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									221.9	210.5	189.9
Contingent Revenue [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									147	135.6	98
Investment income [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									75.9	86.9	70.1
Net (Losses) Gains on Divestitures [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									(5.8)	75.3	10.2
Clean Coal Activities [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									863.5	1,319.3	1,746.3
Other Net (Losses) Gains [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									(0.4)	(2.9)	0.9
Brokerage [Member]
Segment Reporting Information [Line Items]
Goodwill - net	6,053.6				5,548.9				6,053.6	5,548.9	4,573.6
Brokerage [Member] \| Unites States [Member]
Segment Reporting Information [Line Items]
Goodwill - net	3,399.8				3,163.8				3,399.8	3,163.8
Brokerage [Member] \| United Kingdom [Member]
Segment Reporting Information [Line Items]
Goodwill - net	1,328.3				1,177.8				1,328.3	1,177.8
Brokerage [Member] \| Australia [Member]
Segment Reporting Information [Line Items]
Goodwill - net	462.1				416.5				462.1	416.5
Brokerage [Member] \| Canada [Member]
Segment Reporting Information [Line Items]
Goodwill - net	492.9				454.4				492.9	454.4
Brokerage [Member] \| New Zealand [Member]
Segment Reporting Information [Line Items]
Goodwill - net	221.9				208				221.9	208
Brokerage [Member] \| Other Foreign [Member]
Segment Reporting Information [Line Items]
Goodwill - net	148.6				128.4				148.6	128.4
Brokerage [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									5,167.1	4,901.5	4,246.9
Total revenues									5,167.1	4,901.5	4,246.9
Compensation									2,882.5	2,745.9	2,447.1
Operating									687.2	796.5	673.5
Depreciation									73.5	66.6	60.9
Amortization									411.3	329.1	286.9
Change in estimated acquisition earnout payables									(29.7)	16.9	14.3
Total expenses									4,024.8	3,955	3,482.7
Earnings (loss) before income taxes									1,142.3	946.5	764.2
Provision (benefit) for income taxes									276.3	229.2	191
Net earnings (loss)									866	717.3	573.2
Net earnings attributable to noncontrolling interests									4.9	17.2	10.7
Net earnings (loss) attributable to controlling interests									861.1	700.1	562.5
Net foreign exchange (loss) gain									(2.6)	(1)
Total identifiable assets	19,185.3				16,741.9				19,185.3	16,741.9	13,785.1
Goodwill - net	6,053.6				5,548.9				6,053.6	5,548.9	4,573.6
Amortizable intangible assets - net	2,376.3				2,289.9				2,376.3	2,289.9	1,753.7
Brokerage [Member] \| Operating Segments [Member] \| Unites States [Member]
Segment Reporting Information [Line Items]
Total revenues									3,369.4	3,234.3	2,840.9
Total identifiable assets	8,897.9				8,132.3				8,897.9	8,132.3	6,865.4
Brokerage [Member] \| Operating Segments [Member] \| United Kingdom [Member]
Segment Reporting Information [Line Items]
Total revenues									993.7	921.8	738.5
Total identifiable assets	6,135.1				4,964.5				6,135.1	4,964.5	3,758.5
Brokerage [Member] \| Operating Segments [Member] \| Australia [Member]
Segment Reporting Information [Line Items]
Total revenues									216.1	211.3	195.9
Total identifiable assets	1,373.3				1,217.9				1,373.3	1,217.9	1,096.1
Brokerage [Member] \| Operating Segments [Member] \| Canada [Member]
Segment Reporting Information [Line Items]
Total revenues									243.8	221.4	181.1
Total identifiable assets	1,053.6				913.6				1,053.6	913.6	783.1
Brokerage [Member] \| Operating Segments [Member] \| New Zealand [Member]
Segment Reporting Information [Line Items]
Total revenues									141.8	145.6	141.7
Total identifiable assets	766				695.9				766	695.9	688.5
Brokerage [Member] \| Operating Segments [Member] \| Other Foreign [Member]
Segment Reporting Information [Line Items]
Total revenues									202.3	167.1	148.8
Total identifiable assets	959.4				817.7				959.4	817.7	593.5
Brokerage [Member] \| Commissions [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									3,591.9	3,320.6	2,920.7
Brokerage [Member] \| Broker Fees [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									1,136.9	1,074.2	958.5
Brokerage [Member] \| Supplemental Revenue [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									221.9	210.5	189.9
Brokerage [Member] \| Contingent Revenue [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									147	135.6	98
Brokerage [Member] \| Investment income [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									75.2	85.3	69.6
Brokerage [Member] \| Net (Losses) Gains on Divestitures [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									(5.8)	75.3	10.2
Risk Management [Member]
Segment Reporting Information [Line Items]
Goodwill - net	70.5				66.6				70.5	66.6	49.3
Risk Management [Member] \| Unites States [Member]
Segment Reporting Information [Line Items]
Goodwill - net	33.2				33.1				33.2	33.1
Risk Management [Member] \| United Kingdom [Member]
Segment Reporting Information [Line Items]
Goodwill - net	15.1				12.9				15.1	12.9
Risk Management [Member] \| Australia [Member]
Segment Reporting Information [Line Items]
Goodwill - net	11.5				10.5				11.5	10.5
Risk Management [Member] \| New Zealand [Member]
Segment Reporting Information [Line Items]
Goodwill - net	10.7				10.1				10.7	10.1
Risk Management [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									821.7	838.5	798.3
Reimbursements									151.7	138.6	141.6
Total revenues									973.4	977.1	939.9
Compensation									517.5	515.7	489.7
Operating									162.6	184.9	174.6
Reimbursements									151.7	138.6	141.6
Depreciation									49.4	46.2	38.7
Amortization									6	4.9	4.3
Change in estimated acquisition earnout payables									(3.2)	(1.6)	(4.7)
Total expenses									884	888.7	844.2
Earnings (loss) before income taxes									89.4	88.4	95.7
Provision (benefit) for income taxes									22.5	22.2	25.3
Net earnings (loss)									66.9	66.2	70.4
Net earnings (loss) attributable to controlling interests									66.9	66.2	70.4
Net foreign exchange (loss) gain									(0.1)	(0.1)
Total identifiable assets	973.9				898.1				973.9	898.1	748.1
Goodwill - net	70.5				66.6				70.5	66.6	49.3
Amortizable intangible assets - net	23.6				28.8				23.6	28.8	19.3
Risk Management [Member] \| Operating Segments [Member] \| Unites States [Member]
Segment Reporting Information [Line Items]
Total revenues									816.4	828.4	789.7
Total identifiable assets	716.2				655.6				716.2	655.6	571.4
Risk Management [Member] \| Operating Segments [Member] \| United Kingdom [Member]
Segment Reporting Information [Line Items]
Total revenues									40.7	41.6	35.4
Total identifiable assets	139.2				126.6				139.2	126.6	103.8
Risk Management [Member] \| Operating Segments [Member] \| Australia [Member]
Segment Reporting Information [Line Items]
Total revenues									98.4	87.3	94.7
Total identifiable assets	89.6				90				89.6	90	47.2
Risk Management [Member] \| Operating Segments [Member] \| Canada [Member]
Segment Reporting Information [Line Items]
Total revenues									5.3	4.6	4.3
Total identifiable assets	4.8				3.1				4.8	3.1	4.4
Risk Management [Member] \| Operating Segments [Member] \| New Zealand [Member]
Segment Reporting Information [Line Items]
Total revenues									12.6	15.2	15.8
Total identifiable assets	24.1				22.8				24.1	22.8	21.3
Risk Management [Member] \| Broker Fees [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									821	836.9	797.8
Risk Management [Member] \| Investment income [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									0.7	1.6	0.5
Corporate [Member]
Segment Reporting Information [Line Items]
Goodwill - net	2.9				3				2.9	3	2.7
Corporate [Member] \| Other Foreign [Member]
Segment Reporting Information [Line Items]
Goodwill - net	2.9				3				2.9	3
Corporate [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									863.1	1,316.4	1,747.2
Total revenues									863.1	1,316.4	1,747.2
Compensation									66.5	77.9	89.5
Operating									56.7	87.1	55.6
Cost of revenues from clean coal activities									882.1	1,352.8	1,816
Interest									196.4	179.8	138.4
Depreciation									22.2	27.6	28.2
Total expenses									1,223.9	1,725.2	2,127.7
Earnings (loss) before income taxes									(360.8)	(408.8)	(380.5)
Provision (benefit) for income taxes									(286)	(341.1)	(412.8)
Net earnings (loss)									(74.8)	(67.7)	32.3
Net earnings attributable to noncontrolling interests									34.4	29.8	31.7
Net earnings (loss) attributable to controlling interests									(109.2)	(97.5)	0.6
Net foreign exchange (loss) gain									(0.2)	(5.6)	2.9
Total identifiable assets	2,172.2				1,994.8				2,172.2	1,994.8	1,800.8
Goodwill - net	2.9				3				2.9	3	2.7
Corporate [Member] \| Operating Segments [Member] \| Unites States [Member]
Segment Reporting Information [Line Items]
Total revenues									863.1	1,316.4	1,747.2
Total identifiable assets	$ 2,172.2				$ 1,994.8				2,172.2	1,994.8	1,800.8
Corporate [Member] \| Clean Coal Activities [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									863.5	1,319.3	1,746.3
Corporate [Member] \| Other Net (Losses) Gains [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues before reimbursements									$ (0.4)	$ (2.9)	$ 0.9

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 8.7	$ 10	$ 13.5
Amounts Recorded in Earnings	6.6	4.2	5.8
Adjustments	(5.2)	(5.5)	(9.3)
Balance at End of Year	10.1	8.7	10
Allowance for Estimated Policy Cancellations [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	8.3	7.8	7.4
Amounts Recorded in Earnings	4.1	0.5	(1.2)
Adjustments	(2.5)		1.6
Balance at End of Year	9.9	8.3	7.8
Valuation Allowance for Deferred Tax Assets [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	80.5	67.4	79.1
Amounts Recorded in Earnings	14.4	13.1	(11.7)
Balance at End of Year	94.9	80.5	67.4
Accumulated Amortization of Expiration Lists, Non-compete Agreements and Trade Names [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	2,087.5	1,750.4	1,490.7
Amounts Recorded in Earnings	417.3	334	291.2
Adjustments	32.2	3.1	(31.5)
Balance at End of Year	$ 2,537	$ 2,087.5	$ 1,750.4