Securities - Realized Gains and Losses on Investment Securities Transactions Attributable to Available-for-sale Securities (Detail) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
|
| Investments, Debt and Equity Securities [Abstract] | ||||
| Gross realized gains | $ 9 | $ 7 | $ 20 | $ 10 |
| Gross realized losses | 0 | (1) | 0 | (1) |
| Net realized gains | $ 9 | $ 6 | $ 20 | $ 9 |