Collateralized Agreements and Financings - Financial Instruments Received as Collateral and Repledged (Parenthetical) (Detail) - USD ($) $ in Millions |
Jun. 30, 2021 |
Dec. 31, 2020 |
|---|---|---|
| Collateralized Agreements And Financings [Abstract] | ||
| Securities segregated for regulatory and other purposes | $ 23,870 | $ 32,970 |