Fair Value Measurements (Assets and Liabilities Measured on a Recurring Basis) (Details) - USD ($) $ in Millions | 3 Months Ended | | |
Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2022 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Investments, Fair Value Disclosure | $ 743.8 | $ 825.5 | $ 740.8 | $ 794.9 |
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Investments, Fair Value Disclosure | 49 | | 51.7 | |
Foreign currency forward contracts receivable | 0 | | 0 | |
Loans Receivable, Fair Value Disclosure | 0 | | 0 | |
Deferred compensation plan assets | 0 | | 0 | |
Mortgage banking derivative asset | 0 | | 0 | |
Total assets at fair value | 49 | | 51.7 | |
Foreign currency forward contracts payable | 0 | | 0 | |
Deferred compensation plan liabilities | 0 | | 0 | |
Business Combination, Contingent Consideration, Liability | 0 | | 0 | |
Mortgage banking derivative liabilities | 0 | | 0 | |
Total liabilities at fair value | 0 | | 0 | |
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Investments, Fair Value Disclosure | 0 | | 0 | |
Foreign currency forward contracts receivable | 3.8 | | 12.5 | |
Loans Receivable, Fair Value Disclosure | 322.4 | | 677.4 | |
Deferred compensation plan assets | 627.1 | | 604.3 | |
Mortgage banking derivative asset | 0 | | 0 | |
Total assets at fair value | 953.3 | | 1,294.2 | |
Foreign currency forward contracts payable | 10.3 | | 8.8 | |
Deferred compensation plan liabilities | 589.9 | | 576.1 | |
Business Combination, Contingent Consideration, Liability | 0 | | 0 | |
Mortgage banking derivative liabilities | 0 | | 0 | |
Total liabilities at fair value | 600.2 | | 584.9 | |
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Derivative Assets (Liabilities), at Fair Value, Net | 18.9 | 12.8 | 10.3 | 20.7 |
Investments, Fair Value Disclosure | 369.7 | 73.1 | 367.3 | 452 |
Foreign currency forward contracts receivable | 0 | | 0 | |
Loans Receivable, Fair Value Disclosure | 0 | | 0 | |
Deferred compensation plan assets | 0 | | 0 | |
Mortgage banking derivative asset | 139.3 | | 128 | |
Total assets at fair value | 509 | | 495.3 | |
Foreign currency forward contracts payable | 0 | | 0 | |
Deferred compensation plan liabilities | 0 | | 0 | |
Business Combination, Contingent Consideration, Liability | 46.7 | 466.5 | 57.5 | $ 73.2 |
Mortgage banking derivative liabilities | 120.4 | | 117.7 | |
Total liabilities at fair value | 167.1 | | $ 175.2 | |
Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings | (1.1) | 4.9 | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) | (0.2) | 0.5 | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | 0.5 | 9.1 | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements | 0 | 0 | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 3.2 | | | |
Derivative [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings | 8.7 | (5) | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) | 0 | 0 | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | 23.8 | 31.1 | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements | (23.9) | (34) | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 0 | | | |
Earn-out Liabilities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member] | | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings | (10.5) | 0 | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) | 0 | 0.2 | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | 0 | 0 | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements | (0.3) | $ (0.3) | | |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | $ 0 | | | |