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 |
Dec. 31, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Deposits at Fair Value [Member] | ||
| Derivative Instruments and Hedging Activities Disclosures [Line Items] | ||
| Carrying Amount | $ 17,303 | $ 19,634 |
| Cumulative Hedging Adjustment | 649 | 200 |
| Unsecured short-term borrowings [Member] | ||
| Derivative Instruments and Hedging Activities Disclosures [Line Items] | ||
| Carrying Amount | 5,976 | 6,008 |
| Cumulative Hedging Adjustment | 53 | 28 |
| Unsecured long-term borrowings [Member] | ||
| Derivative Instruments and Hedging Activities Disclosures [Line Items] | ||
| Carrying Amount | 115,242 | 87,874 |
| Cumulative Hedging Adjustment | $ 11,624 | $ 7,292 |