Investment Securities - Investment Securities in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	$ 3,526	$ 8,966
AFS, less than 12 months, gross unrealized losses	22	107
AFS, 12 months or longer, fair value	3,590	4,243
AFS, 12 months or longer, gross unrealized losses	99	132
Total investment securities, less than 12 months, fair value	4,380	10,051
Total investment securities, less than 12 months, gross unrealized losses	28	127
Total investment securities, 12 months or longer, fair value	14,724	16,013
Total investment securities, 12 months or longer, gross unrealized losses	1,145	1,361
Schedule of Held-to-Maturity Securities [Line Items]
HTM, less than 12 months, fair value	854	1,085
HTM, Less than 12 months, gross unrealized losses	6	20
HTM, 12 months or longer, fair value	11,134	11,770
HTM, 12 months or longer, gross unrealized losses	1,046	1,229
U.S. Treasury
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	814	1,971
AFS, less than 12 months, gross unrealized losses	1	9
AFS, 12 months or longer, fair value	2,014	2,554
AFS, 12 months or longer, gross unrealized losses	10	18
Schedule of Held-to-Maturity Securities [Line Items]
HTM, less than 12 months, fair value	50	50
HTM, Less than 12 months, gross unrealized losses	0	0
HTM, 12 months or longer, fair value	382	951
HTM, 12 months or longer, gross unrealized losses	10	14
Commercial
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	1,362	2,566
AFS, less than 12 months, gross unrealized losses	11	45
AFS, 12 months or longer, fair value	26	64
AFS, 12 months or longer, gross unrealized losses	0	0
Schedule of Held-to-Maturity Securities [Line Items]
HTM, less than 12 months, fair value	0	0
HTM, Less than 12 months, gross unrealized losses	0	0
HTM, 12 months or longer, fair value	1,921	1,877
HTM, 12 months or longer, gross unrealized losses	114	157
Residential
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	1,349	4,429
AFS, less than 12 months, gross unrealized losses	10	53
AFS, 12 months or longer, fair value	1,548	1,623
AFS, 12 months or longer, gross unrealized losses	89	114
Schedule of Held-to-Maturity Securities [Line Items]
HTM, less than 12 months, fair value	764	996
HTM, Less than 12 months, gross unrealized losses	5	19
HTM, 12 months or longer, fair value	6,761	6,811
HTM, 12 months or longer, gross unrealized losses	795	942
Other
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	1	0
AFS, less than 12 months, gross unrealized losses	0	0
AFS, 12 months or longer, fair value	2	2
AFS, 12 months or longer, gross unrealized losses	0	0
State and political subdivisions
Schedule of Held-to-Maturity Securities [Line Items]
HTM, less than 12 months, fair value	40	39
HTM, Less than 12 months, gross unrealized losses	1	1
HTM, 12 months or longer, fair value	2,070	2,131
HTM, 12 months or longer, gross unrealized losses	$ 127	$ 116