Investment securities - Net Securities Gains (Losses) (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
|
| Securities [Abstract] | ||||
| Realized gross gains | $ 3 | $ 5 | $ 8 | $ 9 |
| Realized gross losses | (28) | (40) | (83) | (44) |
| Total net investment securities gains (losses) | $ (25) | $ (35) | $ (75) | $ (35) |