Securities - Additional Information (Detail) - USD ($)		3 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, allowance for credit losses				$ 1,000,000	$ 1,000,000	[1]
Securities held-to-maturity, allowance for credit losses	[1]			1,000,000	2,000,000
Securities held-to-maturity, nonaccrual				0	0
Equity securities without readily determinable fair values, impairment loss adjustment		$ 3,000,000	$ 2,000,000
Financial Asset, Past Due [Member]
Debt Securities, Available-for-sale [Line Items]
Securities held-to-maturity, past due				0	0
Other assets [Member]
Debt Securities, Available-for-sale [Line Items]
Equity securities carried at fair value				289,000,000	284,000,000
Equity securities without readily determinable fair values				16,000,000	14,000,000
Federal Home Loan Bank Stock				110,000,000	259,000,000
Federal Reserve Bank Stock				$ 558,000,000	$ 559,000,000

[1] See Note 5, "Securities," for additional information regarding the allowance for credit losses associated with our security portfolios.