| Shareholder Report | 6 Months Ended |
| Oct. 31, 2024 USD ($) Holding |
| Shareholder Report [Line Items] | | |
| Document Type | N-CSRS | |
| 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 | Oct. 31, 2024 | |
| Columbia U.S. Treasury Index Fund - Class A | | |
| Shareholder Report [Line Items] | | |
| Fund Name | Columbia U.S. Treasury Index Fund | |
| Class Name | Class A | |
| Trading Symbol | LUTAX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-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 Class A $ 0.32 % (a) (a) Annualized. | |
| Expenses Paid, Amount | $ 17 | |
| Expense Ratio, Percent | 0.32% | [1] |
| Net Assets | $ 864,791,980 | |
| Holdings Count | Holding | 274 | |
| Investment Company, Portfolio Turnover | 21% | |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets $ Total number of portfolio holdings 274 Portfolio turnover for the reporting period 21% | |
| 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. Bond ratings on Fund holdings are divided into categories ranging from highest to lowest credit quality, determined by using the middle rating of Moody’s Ratings, S&P and Fitch, after dropping the highest and lowest available ratings. When ratings are available from only two rating agencies, the lower rating is used. When a rating is available from only one rating agency, that rating is used. If a security is not rated by Moody's Ratings, S&P or Fitch, but has a rating by Kroll and/or DBRS, the same methodology is applied to those bonds that would otherwise be not rated. When a bond is not rated by any rating agency, it is designated as “Not rated.” Credit quality ratings assigned by a rating agency are subjective opinions, not statements of fact, and are subject to change, including daily. Top Holdings U.S. Treasury 1.2 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % Asset Categories Credit Quality | |
| Credit Quality Explanation [Text Block] | Bond ratings on Fund holdings are divided into categories ranging from highest to lowest credit quality, determined by using the middle rating of Moody’s Ratings, S&P and Fitch, after dropping the highest and lowest available ratings. When ratings are available from only two rating agencies, the lower rating is used. When a rating is available from only one rating agency, that rating is used. If a security is not rated by Moody's Ratings, S&P or Fitch, but has a rating by Kroll and/or DBRS, the same methodology is applied to those bonds that would otherwise be not rated. When a bond is not rated by any rating agency, it is designated as “Not rated.” Credit quality ratings assigned by a rating agency are subjective opinions, not statements of fact, and are subject to change, including daily. | |
| Largest Holdings [Text Block] | Top Holdings U.S. Treasury 1.2 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % | |
| Columbia U.S. Treasury Index Fund - Institutional Class | | |
| Shareholder Report [Line Items] | | |
| Fund Name | Columbia U.S. Treasury Index Fund | |
| Class Name | Institutional Class | |
| Trading Symbol | IUTIX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-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 $ 0.17 % (a) (a) Annualized. | |
| Expenses Paid, Amount | $ 9 | |
| Expense Ratio, Percent | 0.17% | [1] |
| Net Assets | $ 864,791,980 | |
| Holdings Count | Holding | 274 | |
| Investment Company, Portfolio Turnover | 21% | |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets $ Total number of portfolio holdings 274 Portfolio turnover for the reporting period 21% | |
| Holdings [Text Block] | Graphical Representation of Fund Holdings 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. Bond ratings on Fund holdings are divided into categories ranging from highest to lowest credit quality Top Holdings U.S. Treasury 1.2 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % Asset Categories Credit Quality | |
| Credit Quality Explanation [Text Block] | Bond ratings on Fund holdings are divided into categories ranging from highest to lowest credit quality | |
| Largest Holdings [Text Block] | Top Holdings U.S. Treasury 1.2 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % | |
| Columbia U.S. Treasury Index Fund - Institutional 2 Class | | |
| Shareholder Report [Line Items] | | |
| Fund Name | Columbia U.S. Treasury Index Fund | |
| Class Name | Institutional 2 Class | |
| Trading Symbol | CUTRX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-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 2 Class $ 0.17 % (a) (a) Annualized. | |
| Expenses Paid, Amount | $ 9 | |
| Expense Ratio, Percent | 0.17% | [1] |
| Net Assets | $ 864,791,980 | |
| Holdings Count | Holding | 274 | |
| Investment Company, Portfolio Turnover | 21% | |
| Additional Fund Statistics [Text Block] | Key Fund Sta tisti Fund net assets $ Total number of portfolio holdings 274 Portfolio turnover for the reporting period 21% | |
| 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. Bond ratings on Fund holdings are divided into categories ranging from highest to lowest credit quality, determined by using the middle rating of Moody’s Ratings, S&P and Fitch, after dropping the highest and lowest available ratings. When ratings are available from only two rating agencies, the lower rating is used. When a rating is available from only one rating agency, that rating is used. If a security is not rated by Moody's Ratings, S&P or Fitch, but has a rating by Kroll and/or DBRS, the same methodology is applied to those bonds that would otherwise be not rated. When a bond is not rated by any rating agency, it is designated as “Not rated.” Credit quality ratings assigned by a rating agency are subjective opinions, not statements of fact, and are subject to change, including daily. Top Holdings U.S. Treasury 1.2 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % Asset Categories Credit Quality | |
| Credit Quality Explanation [Text Block] | Bond ratings on Fund holdings are divided into categories ranging from highest to lowest credit quality, determined by using the middle rating of Moody’s Ratings, S&P and Fitch, after dropping the highest and lowest available ratings. When ratings are available from only two rating agencies, the lower rating is used. When a rating is available from only one rating agency, that rating is used. If a security is not rated by Moody's Ratings, S&P or Fitch, but has a rating by Kroll and/or DBRS, the same methodology is applied to those bonds that would otherwise be not rated. When a bond is not rated by any rating agency, it is designated as “Not rated.” Credit quality ratings assigned by a rating agency are subjective opinions, not statements of fact, and are subject to change, including daily. | |
| Largest Holdings [Text Block] | Top Holdings U.S. Treasury 1.2 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % | |
| Columbia U.S. Treasury Index Fund - Institutional 3 Class | | |
| Shareholder Report [Line Items] | | |
| Fund Name | Columbia U.S. Treasury Index Fund | |
| Class Name | Institutional 3 Class | |
| Trading Symbol | CUTYX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-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 3 Class $ 0.17 % (a) (a) Annualized. | |
| Expenses Paid, Amount | $ 9 | |
| Expense Ratio, Percent | 0.17% | [1] |
| Net Assets | $ 864,791,980 | |
| Holdings Count | Holding | 274 | |
| Investment Company, Portfolio Turnover | 21% | |
| Additional Fund Statistics [Text Block] | Key Fund Statistics Fund net assets $ Total number of portfolio holdings 274 Portfolio turnover for the reporting period 21% | |
| 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. Bond ratings on Fund holdings are divided into categories ranging from highest to lowest credit quality, determined by using the middle rating of Moody’s Ratings, S&P and Fitch, after dropping the highest and lowest available ratings. When ratings are available from only two rating agencies, the lower rating is used. When a rating is available from only one rating agency, that rating is used. If a security is not rated by Moody's Ratings, S&P or Fitch, but has a rating by Kroll and/or DBRS, the same methodology is applied to those bonds that would otherwise be not rated. When a bond is not rated by any rating agency, it is designated as Top Holdings U.S. Treasury 1.2 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % Asset Categories Credit Quality | |
| Credit Quality Explanation [Text Block] | Bond ratings on Fund holdings are divided into categories ranging from highest to lowest credit quality, determined by using the middle rating of Moody’s Ratings, S&P and Fitch, after dropping the highest and lowest available ratings. When ratings are available from only two rating agencies, the lower rating is used. When a rating is available from only one rating agency, that rating is used. If a security is not rated by Moody's Ratings, S&P or Fitch, but has a rating by Kroll and/or DBRS, the same methodology is applied to those bonds that would otherwise be not rated. When a bond is not rated by any rating agency, it is designated as | |
| Largest Holdings [Text Block] | Top Holdings U.S. Treasury 1.2 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.9 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % U.S. Treasury 0.8 % | |
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| [1]Annualized. |
