Securities - Additional Information (Detail) - USD ($)		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, allowance for credit losses	[1]	$ 1,000,000		$ 1,000,000
Securities held-to-maturity, allowance for credit losses	[1]	2,000,000		2,000,000
Securities held-to-maturity, past due		0		0
Securities held-to-maturity, nonaccrual		0		0
Equity securities without readily determinable fair values, impairment loss adjustment		0	$ 0
Other assets [Member]
Debt Securities, Available-for-sale [Line Items]
Equity securities carried at fair value		282,000,000		284,000,000
Equity securities without readily determinable fair values		14,000,000		14,000,000
Federal Home Loan Bank Stock		192,000,000		259,000,000
Federal Reserve Bank Stock		$ 559,000,000		$ 559,000,000

[1] See Note 4, "Securities," for additional information regarding the allowance for credit losses associated with our security portfolios.