Securities - Narrative (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, allowance for credit losses	$ 0		$ 0		$ 0
Securities held-to-maturity, allowance for credit losses	0		0		0
Securities held-to-maturity	18,265,000,000		18,265,000,000		17,798,000,000
Debt securities, available-for-sale, realized loss	0	$ 149,000,000	1,000,000	$ 153,000,000
Securities held-to-maturity, nonaccrual	0		0		0
Equity securities without readily determinable fair values, impairment loss adjustment			4,000,000	$ 4,000,000
U.S. Government sponsored mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, carrying value		2,130,000,000
Debt securities, available-for-sale, realized loss		$ 148,000,000
Total Past Due 30 Days or More
Debt Securities, Available-for-sale [Line Items]
Securities held-to-maturity	0		0		0
Other assets
Debt Securities, Available-for-sale [Line Items]
Federal Home Loan Bank stock	95,000,000		95,000,000		95,000,000
Federal Reserve Bank stock	$ 437,000,000		$ 437,000,000		$ 438,000,000