Shareholder Report |
12 Months Ended | ||||||||||||||||||||
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Apr. 30, 2025
USD ($)
Holding
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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 | Apr. 30, 2025 | ||||||||||||||||||||
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 annual shareholder report contains important information about Columbia U.S. Treasury Index Fund (the Fund) for the period of May 1, 2024 to April 30, 2025. | ||||||||||||||||||||
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 . You can also request more information by contacting us at 1-800-345-6611.
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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)
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Expenses Paid, Amount | $ 33 | ||||||||||||||||||||
Expense Ratio, Percent | 0.32% | ||||||||||||||||||||
Factors Affecting Performance [Text Block] | Management's Discussion of Fund Performance The performance of Class A shares for the period presented is shown in the Average Annual Total Returns table. Top Performance Contributors Allocation | Performance was driven by intermediate maturity U.S. Treasuries, as 3-5 Yr Treasuries returned 8.56% and 5-10 year Treasuries returned 9.02%, both outperforming shorter and longer maturity issues.Yield curve | The yield curve steepened over the year, with yields on all Treasuries under 5-years falling at least 1.00%, all of which benefited from the corresponding price appreciation. Treasuries longer than seven years also experienced lower yields but by a smaller margin, the longer the bond’s maturity.Top Performance Detractors Allocation | 1-3 year Treasuries, which made up one-third of the Fund’s portfolio, posted positive returns of 6.68% during the annual period, but contributed less to overall performance. U.S. Treasuries longer than 10 years, approximately 20% of the Fund’s portfolio, returned 4.89% for the same period. |
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Performance Past Does Not Indicate Future [Text] | The Fund's past performance is not a good predictor of the Fund's future performance. | ||||||||||||||||||||
Line Graph [Table Text Block] | ![]() |
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Average Annual Return [Table Text Block] |
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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 performance to the Bloomberg U.S. Aggregate Bond Index, a broad-based performance index, as required by new regulatory requirements. | ||||||||||||||||||||
Prior Market Index Comparison [Text Block] | The Fund’s performance also continues to be compared to its prior benchmarks, which management believes 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 for more recent performance information.
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Net Assets | $ 817,580,549 | ||||||||||||||||||||
Holdings Count | Holding | 275 | ||||||||||||||||||||
Advisory Fees Paid, Amount | $ 3,412,975 | ||||||||||||||||||||
Investment Company, Portfolio Turnover | 42.00% | ||||||||||||||||||||
Additional Fund Statistics [Text Block] | Key Fund Statistics
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Holdings [Text Block] | Graphical Representation of FundThe 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
Asset Categories ![]() Credit Quality ![]() |
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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
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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 annual shareholder report contains important information about Columbia U.S. Treasury Index Fund (the Fund) for the period of May 1, 2024 to April 30, 2025. | ||||||||||||||||||||
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 . You can also request more information by contacting us at 1-800-345-6611.
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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)
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Expenses Paid, Amount | $ 18 | ||||||||||||||||||||
Expense Ratio, Percent | 0.17% | ||||||||||||||||||||
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 Allocation | Performance was driven by intermediate maturity U.S. Treasuries, as 3-5 Yr Treasuries returned 8.56% and 5-10 year Treasuries returned 9.02%, both outperforming shorter and longer maturity issues.Yield curve | The yield curve steepened over the year, with yields on all Treasuries under 5-years falling at least 1.00%, all of which benefited from the corresponding price appreciation. Treasuries longer than seven years also experienced lower yields but by a smaller margin, the longer the bond’s maturity.Top Performance Detractors Allocation | 1-3 year Treasuries, which made up one-third of the Fund’s portfolio, posted positive returns of 6.68% during the annual period, but contributed less to overall performance. U.S. Treasuries longer than 10 years, approximately 20% of the Fund’s portfolio, returned 4.89% for the same period. |
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Performance Past Does Not Indicate Future [Text] | The Fund's past performance is not a good predictor of the Fund's future performance. | ||||||||||||||||||||
Line Graph [Table Text Block] | ![]() |
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Average Annual Return [Table Text Block] |
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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 performance to the Bloomberg U.S. Aggregate Bond Index, a broad-based performance index, as required by new regulatory requirements. | ||||||||||||||||||||
Prior Market Index Comparison [Text Block] | The Fund’s performance also continues to be compared to its prior benchmarks, which management believes 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 for more recent performance information.
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Net Assets | $ 817,580,549 | ||||||||||||||||||||
Holdings Count | Holding | 275 | ||||||||||||||||||||
Advisory Fees Paid, Amount | $ 3,412,975 | ||||||||||||||||||||
Investment Company, Portfolio Turnover | 42.00% | ||||||||||||||||||||
Additional Fund Statistics [Text Block] | Key Fund Statistics
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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
Asset Categories ![]() Credit Quality ![]() |
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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
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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 annual shareholder report contains important information about Columbia U.S. Treasury Index Fund (the Fund) for the period of May 1, 2024 to April 30, 2025. | ||||||||||||||||||||
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 . You can also request more information by contacting us at 1-800-345-6611.
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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)
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Expenses Paid, Amount | $ 18 | ||||||||||||||||||||
Expense Ratio, Percent | 0.17% | ||||||||||||||||||||
Factors Affecting Performance [Text Block] | Management's Discussion of Fund Performance The performance of Institutional 2 Class shares for the period presented is shown in the Average Annual Total Returns table. Top Performance Contributors Allocation | Performance was driven by intermediate maturity U.S. Treasuries, as 3-5 Yr Treasuries returned 8.56% and 5-10 year Treasuries returned 9.02%, both outperforming shorter and longer maturity issues.Yield curve | The yield curve steepened over the year, with yields on all Treasuries under 5-years falling at least 1.00%, all of which benefited from the corresponding price appreciation. Treasuries longer than seven years also experienced lower yields but by a smaller margin, the longer the bond’s maturity.Top Performance Detractors Allocation | 1-3 year Treasuries, which made up one-third of the Fund’s portfolio, posted positive returns of 6.68% during the annual period, but contributed less to overall performance. U.S. Treasuries longer than 10 years, approximately 20% of the Fund’s portfolio, returned 4.89% for the same period. |
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Performance Past Does Not Indicate Future [Text] | The Fund's past performance is not a good predictor of the Fund's future performance. | ||||||||||||||||||||
Line Graph [Table Text Block] | ![]() |
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Average Annual Return [Table Text Block] |
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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 performance to the Bloomberg U.S. Aggregate Bond Index, a broad-based performance index, as required by new regulatory requirements. | ||||||||||||||||||||
Prior Market Index Comparison [Text Block] | The Fund’s performance also continues to be compared to its prior benchmarks, which management believes 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 for more recent performance information.
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Net Assets | $ 817,580,549 | ||||||||||||||||||||
Holdings Count | Holding | 275 | ||||||||||||||||||||
Advisory Fees Paid, Amount | $ 3,412,975 | ||||||||||||||||||||
Investment Company, Portfolio Turnover | 42.00% | ||||||||||||||||||||
Additional Fund Statistics [Text Block] | Key Fund Statistics
|
||||||||||||||||||||
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
Asset Categories ![]() Credit Quality ![]() |
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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
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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 annual shareholder report contains important information about Columbia U.S. Treasury Index Fund (the Fund) for the period of May 1, 2024 to April 30, 2025. | ||||||||||||||||||||
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 . You can also request more information by contacting us at 1-800-345-6611.
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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)
|
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Expenses Paid, Amount | $ 18 | ||||||||||||||||||||
Expense Ratio, Percent | 0.17% | ||||||||||||||||||||
Factors Affecting Performance [Text Block] | Management's Discussion of Fund Performance The performance of Institutional 3 Class shares for the period presented is shown in the Average Annual Total Returns table. Top Performance Contributors Allocation | Performance was driven by intermediate maturity U.S. Treasuries, as 3-5 Yr Treasuries returned 8.56% and 5-10 year Treasuries returned 9.02%, both outperforming shorter and longer maturity issues.Yield curve | The yield curve steepened over the year, with yields on all Treasuries under 5-years falling at least 1.00%, all of which benefited from the corresponding price appreciation. Treasuries longer than seven years also experienced lower yields but by a smaller margin, the longer the bond’s maturity.Top Performance Detractors Allocation | 1-3 year Treasuries, which made up one-third of the Fund’s portfolio, posted positive returns of 6.68% during the annual period, but contributed less to overall performance. U.S. Treasuries longer than 10 years, approximately 20% of the Fund’s portfolio, returned 4.89% for the same period. |
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Performance Past Does Not Indicate Future [Text] | The Fund's past performance is not a good predictor of the Fund's future performance. | ||||||||||||||||||||
Line Graph [Table Text Block] | ![]() |
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Average Annual Return [Table Text Block] |
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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 performance to the Bloomberg U.S. Aggregate Bond Index, a broad-based performance index, as required by new regulatory requirements. | ||||||||||||||||||||
Prior Market Index Comparison [Text Block] | The Fund’s performance also continues to be compared to its prior benchmarks, which management believes 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 for more recent performance information.
|
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Net Assets | $ 817,580,549 | ||||||||||||||||||||
Holdings Count | Holding | 275 | ||||||||||||||||||||
Advisory Fees Paid, Amount | $ 3,412,975 | ||||||||||||||||||||
Investment Company, Portfolio Turnover | 42.00% | ||||||||||||||||||||
Additional Fund Statistics [Text Block] | Key Fund Statistics
|
||||||||||||||||||||
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
Asset Categories ![]() Credit Quality ![]() |
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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
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