| Shareholder Report | 12 Months Ended |
| Aug. 31, 2024 USD ($) Holding |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | Columbia Funds Series Trust I |
| Entity Central Index Key | 0000773757 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Aug. 31, 2024 |
| Multisector Bond SMA Completion Portfolio [Member] | |
| Shareholder Report [Line Items] | |
| Fund Name | Multisector Bond SMA Completion Portfolio |
| Class Name | Multisector Bond SMA Completion Portfolio |
| Trading Symbol | MBSAX |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about Multisector Bond SMA Completion Portfolio (the Fund) for the period of September 1, 2023 to August 31, 2024. |
| Shareholder Report Annual or Semi-Annual | annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at columbiathreadneedleus.com/resources/literature 1-800-345-6611. |
| Additional Information Phone Number | 1-800-345-6611 |
| Additional Information Website | columbiathreadneedleus.com/resources/literature |
| Expenses [Text Block] | What were the Fund costs for the reporting period? (Based on a hypothetical $10,000 investment) Fund Cost of a $10,000 investment Cost paid as a percentage of a $10,000 investment Multisector Bond SMA Completion Portfolio $ 0.00 % |
| Expenses Paid, Amount | $ 0 |
| Expense Ratio, Percent | 0% |
| Factors Affecting Performance [Text Block] | Management's Discussion of Fund Performance The performance of the Fund for the period presented is shown in the Average Annual Total Returns table. Top Performance Contributors Duration Sector allocations Top Performance Detractors Derivatives usage |
| Performance Past Does Not Indicate Future [Text] | Past performance does not guarantee future performance. |
| Line Graph [Table Text Block] | |
| Average Annual Return [Table Text Block] | Average Annual Total Returns (%) 1 year Since Fund Multisector Bond SMA Completion Portfolio 14.90 5.67 Bloomberg U.S. Aggregate Bond Index 7.30 0.15 |
| No Deduction of Taxes [Text Block] | Performance does not reflect the deduction of taxes that a shareholder may pay on fund distributions or on the redemptions of fund shares. |
| Updated Performance Information Location [Text Block] | Visit columbiathreadneedleus.com/investment-products/mutual-funds |
| Net Assets | $ 2,709,504 |
| Holdings Count | Holding | 15 |
| Advisory Fees Paid, Amount | $ 0 |
| Investment Company, Portfolio Turnover | 967% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets $ Total number of portfolio holdings 15 Management services fees $ Portfolio turnover for the reporting period 967% |
| Holdings [Text Block] | Graphical Representation of Fund The tables below show the investment makeup of the Fund represented as a percentage of Fund net assets. Derivatives are excluded from the tables unless otherwise noted. The Fund's portfolio composition is subject to change. Derivative Exposure Long Credit Risk 92.3 % Interest Rate Risk 40.4 % Short Interest Rate Risk 26.5 % Asset Categories |
| Updated Prospectus Web Address | columbiathreadneedleus.com/investment-products/mutual-funds |
