Securities - Additional Information (Detail) - USD ($)		Mar. 31, 2020		Jan. 01, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, allowance for credit losses	[2]	$ 2,000,000	[1]	$ 3,000,000
Securities held-to-maturity, allowance for credit losses	[2]	2,000,000	[1]	2,000,000
Securities held-to-maturity, past due		0		0
Securities held-to-maturity, nonaccrual		0		$ 0
Equity securities without readily determinable fair value, impairment loss		0			$ 0
Other assets [Member]
Debt Securities, Available-for-sale [Line Items]
Equity securities carried at fair value		278,000,000			283,000,000
Equity securities without readily determinable fair values		12,000,000			12,000,000
Federal Home Loan Bank Stock		324,000,000			110,000,000
Federal Reserve Bank Stock		$ 559,000,000			$ 559,000,000

[1] As discussed in Note 21, "New Accounting Pronouncements," beginning January 1, 2020, an allowance for credit losses is recognized for debt securities while, prior to January 1, 2020, debt securities were assessed for other-than-temporary impairment. At December 31, 2019, we did not consider any of our debt securities to be other-than-temporarily impaired

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