| Form N-CSR Cover | 12 Months Ended |
| Aug. 31, 2024 | |
| 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 |
| 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 |
| Multi-Manager Small Cap Equity Strategies Fund Institutional Class | |
| Shareholder Report [Line Items] | |
| Fund Name | Multi-Manager Small Cap Equity Strategies Fund |
| Class Name | Institutional Class |
| Trading Symbol | CZMSX |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about Multi-Manager Small Cap Equity Strategies Fund (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) Class Cost of a $10,000 investment Cost paid as a percentage of a $10,000 investment Institutional Class $ 0.99 % |
| Expenses Paid, Amount | $ 106 |
| Expense Ratio, Percent | 0.99% |
| Factors Affecting Performance [Text Block] | Management's Discussion of Fund Performance The performance of Institutional Class shares for the period presented is shown in the Average Annual Total Returns table. Top Performance Contributors Stock selection Allocations Individual holdings Top Performance Detractors Stock selection Allocations Individual holdings |
| 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 5 years 10 years Institutional Class (a),(b) 14.77 9.77 8.22 Russell ® 18.47 9.68 8.03 Russell ® 26.14 15.19 12.36 (a) The returns shown for periods prior to January 3, 2017 (including returns for the Life of the Fund, if shown, which are since Fund inception) include the returns of Class A. Class A shares were offered prior to the Fund's Institutional Class shares but have since been merged into the Fund’s Institutional Class shares. These returns are adjusted to reflect any higher class-related operating expenses of the newer share classes, as applicable. Please visit columbiathreadneedleus.com/investor/investment-products/mutual-funds/appended-performance (b) Effective August 1, 2024, the Fund compares its performace to the Russell ® |
| 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. |
| Performance Table Market Index Changed [Text Block] | Effective August 1, 2024, the Fund compares its performace to the Russell ® |
| Prior Market Index Comparison [Text Block] | The Fund's performance is also compared to its prior benchmark, which more closely represent the market sectors and/or asset classes in which the Fund primarily invests. |
| Updated Performance Information Location [Text Block] | Visit columbiathreadneedleus.com/investment-products/mutual-funds |
| Net Assets | $ 1,648,637,831 |
| Holdings Count | Holding | 795 |
| Advisory Fees Paid, Amount | $ 12,095,254 |
| Investment Company, Portfolio Turnover | 66% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets $ Total number of portfolio holdings 795 Management services fees $ Portfolio turnover for the reporting period 66% |
| Holdings [Text Block] | Graphical Representation of Fund The tables below show the investment makeup of the Fund represented as a perce ntage of Fun Top Holdings Casella Waste Systems, Inc., Class A 1.6 % Simpson Manufacturing Co., Inc. 1.2 % AAON, Inc. 1.2 % Descartes Systems Group, Inc. (The) 1.1 % Exponent, Inc. 1.0 % SPS Commerce, Inc. 0.8 % Novanta, Inc. 0.8 % FirstService Corp. 0.8 % Altair Engineering, Inc., Class A 0.8 % Construction Partners, Inc., Class A 0.7 % Asset Categories Equity Sector Allocation |
| Largest Holdings [Text Block] | Top Holdings Casella Waste Systems, Inc., Class A 1.6 % Simpson Manufacturing Co., Inc. 1.2 % AAON, Inc. 1.2 % Descartes Systems Group, Inc. (The) 1.1 % Exponent, Inc. 1.0 % SPS Commerce, Inc. 0.8 % Novanta, Inc. 0.8 % FirstService Corp. 0.8 % Altair Engineering, Inc., Class A 0.8 % Construction Partners, Inc., Class A 0.7 % |
| Updated Prospectus Web Address | columbiathreadneedleus.com/investment-products/mutual-funds |
| Shareholder Report, Line Graph (Details) - USD ($) | 12 Months Ended | ||||||||||
| Aug. 31, 2024 | Aug. 31, 2023 | Aug. 31, 2022 | Aug. 31, 2021 | Aug. 31, 2020 | Aug. 31, 2019 | Aug. 31, 2018 | Aug. 31, 2017 | Aug. 31, 2016 | Aug. 31, 2015 | Aug. 31, 2014 | |
| Multi-Manager Small Cap Equity Strategies Fund Institutional Class | |||||||||||
| Account Value [Line Items] | |||||||||||
| Line Graph and Table Measure Name | Institutional Class | ||||||||||
| Account Value | $ 22,024 | $ 19,191 | $ 18,134 | $ 21,477 | $ 14,616 | $ 13,820 | $ 15,858 | $ 12,560 | $ 10,894 | $ 10,190 | $ 10,000 |
| Russell 3000 Index [Member] | |||||||||||
| Account Value [Line Items] | |||||||||||
| Line Graph and Table Measure Name | Russell® 3000 Index | ||||||||||
| Account Value | $ 32,071 | 25,424 | 22,155 | 25,548 | 19,203 | 15,813 | 15,608 | 12,980 | 11,184 | 10,036 | 10,000 |
| Russell 2000 Index [Member] | |||||||||||
| Account Value [Line Items] | |||||||||||
| Line Graph and Table Measure Name | Russell® 2000 Index | ||||||||||
| Account Value | $ 21,655 | $ 18,278 | $ 17,466 | $ 21,270 | $ 14,461 | $ 13,640 | $ 15,659 | $ 12,483 | $ 10,862 | $ 10,003 | $ 10,000 |
| Shareholder Report, Average Annual Return (Details) | 12 Months Ended | 60 Months Ended | 120 Months Ended | |
| Aug. 31, 2024 | Aug. 31, 2024 | Aug. 31, 2024 | ||
| Multi-Manager Small Cap Equity Strategies Fund Institutional Class | ||||
| Average Annual Return [Line Items] | ||||
| Line Graph and Table Measure Name | Institutional Class | |||
| Average Annual Return, Percent | [1],[2] | 14.77% | 9.77% | 8.22% |
| Russell 2000 Index [Member] | ||||
| Average Annual Return [Line Items] | ||||
| Line Graph and Table Measure Name | Russell® 2000 Index | |||
| Average Annual Return, Percent | 18.47% | 9.68% | 8.03% | |
| Russell 3000 Index [Member] | ||||
| Average Annual Return [Line Items] | ||||
| Line Graph and Table Measure Name | Russell® 3000 Index | |||
| Average Annual Return, Percent | 26.14% | 15.19% | 12.36% | |
| [1]Effective August 1, 2024, the Fund compares its performace to the Russell® 3000 Index, a broad-based performance index that meets new regulatory requirements. The Fund's performance is also compared to its prior benchmark, which more closely represent the market sectors and/or asset classes in which the Fund primarily invests.[2]The returns shown for periods prior to January 3, 2017 (including returns for the Life of the Fund, if shown, which are since Fund inception) include the returns of Class A. Class A shares were offered prior to the Fund's Institutional Class shares but have since been merged into the Fund’s Institutional Class shares. These returns are adjusted to reflect any higher class-related operating expenses of the newer share classes, as applicable. Please visit columbiathreadneedleus.com/investor/investment-products/mutual-funds/appended-performance for more information. | ||||
| Shareholder Report, Holdings (Details) - Multi-Manager Small Cap Equity Strategies Fund Institutional Class | Aug. 31, 2024 |
| Casella Waste Systems Inc Class A [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| Simpson Manufacturing Co Inc [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| AAON Inc [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| Descartes Systems Group Inc The [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.10% |
| Exponent Inc [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| SPS Commerce Inc [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Novanta Inc [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| FirstService Corp [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Altair Engineering Inc Class A [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Construction Partners Inc Class A [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.70% |
| Industrial Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 24.10% |
| Financial Services Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.20% |
| Information Technology Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 14.90% |
| Healthcare Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 13.70% |
| Consumer Discretionary Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.20% |
| Energy Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.20% |
| Real Estate Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| Consumer Staples Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| Materials Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| Utilities Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.60% |
| Unclassified Sector [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.80% |
| Common Stocks [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 97.50% |
| Money Market Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
