Regulation and Capital Adequacy - Risk-based Capital (Parenthetical) (Detail) - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
|
| Regulation And Capital Adequacy [Abstract] | ||
| CECL adoption, percentage of increase in regulatory capital to increase in allowance for credit loss | 25.00% | |
| Deferred tax liabilities associated with goodwill | $ 680 | $ 667 |
| Deferred tax liabilities associated with identifiable intangible assets | $ 29 | $ 37 |
| Subordinated debt maturity period | 5 years |