Derivatives and Hedging Activities - Carrying Amount of Hedged Items Currently Designated in a Hedging Relationship and Related Cumulative Hedging Adjustment (Detail) - Derivative Contracts Accounted for as Hedges [Member] - USD ($) $ in Millions |
Sep. 30, 2021 |
Dec. 31, 2020 |
|---|---|---|
| Deposits at Fair Value [Member] | ||
| Derivative Instruments and Hedging Activities Disclosures [Line Items] | ||
| Carrying Amount | $ 15,266 | $ 17,303 |
| Cumulative Hedging Adjustment | 387 | 649 |
| Unsecured short-term borrowings [Member] | ||
| Derivative Instruments and Hedging Activities Disclosures [Line Items] | ||
| Carrying Amount | 3,221 | 5,976 |
| Cumulative Hedging Adjustment | 10 | 53 |
| Unsecured long-term borrowings [Member] | ||
| Derivative Instruments and Hedging Activities Disclosures [Line Items] | ||
| Carrying Amount | 136,905 | 115,242 |
| Cumulative Hedging Adjustment | $ 7,062 | $ 11,624 |