Fair Value Accounting - Aggregate Difference Between Fair Value and UPB for Fair Value Option Loans (Details) - USD ($) $ in Millions |
Jun. 30, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Fair Value Disclosures [Abstract] | ||
| Fair Value, option, loans held as assets, current through 89 days | $ 2,963 | $ 2,244 |
| UPB, option, loans held as assets, current through 89 days | 2,854 | 2,195 |
| Fair value, option, loans held as assets, current through 89 days, aggregate difference | 109 | 49 |
| Fair Value, 90 days or more delinquent | 17 | 0 |
| UPB, op days or more delinquent | 16 | 0 |
| Aggregated difference, 90 days or more delinquent | 1 | 0 |
| Loans held-for-sale, fair value | 2,980 | 2,244 |
| Financing receivable, UPB | 2,870 | 2,195 |
| Fair value option, aggregate difference | $ 110 | $ 49 |