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Business Combinations and Discontinued Operations - Investment Holdings, Other than Securities (Details) - USD ($) $ in Millions | Sep. 30, 2025 | May 18, 2025 | Dec. 31, 2024
--- | --- | --- | ---
Business Combination [Line Items] |  |  |
Total loans held for investment | $ 443,159 |  | $ 327,775
Allowance for credit losses | $ 23,103 |  | $ 16,258
Discover |  |  |
Business Combination [Line Items] |  |  |
Acquired loans held for investment, premium |  | $ 1,100 |
Business combination, fair value of acquired loans held for investment, non-credit discount |  | 1,400 |
Unpaid principal balance |  | 19,400 |
Business combination, expected recovery in allowance for credit losses |  | 3,300 |
Discover | Total |  |  |
Business Combination [Line Items] |  |  |
Unpaid Principal Balance |  | 108,508 |
Premium/(Discount) |  | (334) |
Total loans held for investment |  | 108,174 |
Allowance for credit losses |  | 435 |
Net loans held for investment |  | 108,609 |
Discover | Non-PCD loans |  |  |
Business Combination [Line Items] |  |  |
Unpaid Principal Balance |  | 101,614 |
Premium/(Discount) |  | 1,069 |
Total loans held for investment |  | 102,683 |
Allowance for credit losses |  | 0 |
Net loans held for investment |  | 102,683 |
Discover | PCD loans |  |  |
Business Combination [Line Items] |  |  |
Unpaid Principal Balance |  | 6,894 |
Premium/(Discount) |  | (538) |
Total loans held for investment |  | 6,356 |
Allowance for credit losses |  | 2,870 |
Net loans held for investment |  | 3,486 |
Discover | Recoveries on acquired Discover loans that are fully charged off |  |  |
Business Combination [Line Items] |  |  |
Premium/(Discount) |  | 865 |
Total loans held for investment |  | 865 |
Allowance for credit losses |  | 3,305 |
Net loans held for investment |  | $ 2,440 |

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