Investment Securities - Investment Securities in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	$ 4,786	$ 460
AFS, less than 12 months, gross unrealized losses	36	4
AFS, 12 months or longer, fair value	6,655	9,917
AFS, 12 months or longer, gross unrealized losses	215	247
Total investment securities, less than 12 months, fair value	5,621	2,011
Total investment securities, less than 12 months, gross unrealized losses	50	27
Total investment securities, 12 months or longer, fair value	19,270	21,761
Total investment securities, 12 months or longer, gross unrealized losses	1,492	1,259
Schedule of Held-to-Maturity Securities [Line Items]
HTM, less than 12 months, fair value	835	1,551
HTM, Less than 12 months, gross unrealized losses	14	23
HTM, 12 months or longer, fair value	12,615	11,844
HTM, 12 months or longer, gross unrealized losses	1,277	1,012
U.S. Treasury and federal agencies
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	2,586	229
AFS, less than 12 months, gross unrealized losses	15	1
AFS, 12 months or longer, fair value	4,400	7,474
AFS, 12 months or longer, gross unrealized losses	70	112
Schedule of Held-to-Maturity Securities [Line Items]
HTM, less than 12 months, fair value	0	50
HTM, Less than 12 months, gross unrealized losses	0	0
HTM, 12 months or longer, fair value	980	924
HTM, 12 months or longer, gross unrealized losses	30	31
Commercial
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	1,061	74
AFS, less than 12 months, gross unrealized losses	10	1
AFS, 12 months or longer, fair value	317	330
AFS, 12 months or longer, gross unrealized losses	6	8
Schedule of Held-to-Maturity Securities [Line Items]
HTM, less than 12 months, fair value	0	328
HTM, Less than 12 months, gross unrealized losses	0	9
HTM, 12 months or longer, fair value	1,880	1,575
HTM, 12 months or longer, gross unrealized losses	157	121
Residential
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	1,129	151
AFS, less than 12 months, gross unrealized losses	11	2
AFS, 12 months or longer, fair value	1,874	1,959
AFS, 12 months or longer, gross unrealized losses	137	116
Schedule of Held-to-Maturity Securities [Line Items]
HTM, less than 12 months, fair value	790	955
HTM, Less than 12 months, gross unrealized losses	13	11
HTM, 12 months or longer, fair value	7,510	7,139
HTM, 12 months or longer, gross unrealized losses	959	791
Other debt securities
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	10	6
AFS, less than 12 months, gross unrealized losses	0	0
AFS, 12 months or longer, fair value	64	154
AFS, 12 months or longer, gross unrealized losses	2	11
Obligations of states and political subdivisions
Schedule of Held-to-Maturity Securities [Line Items]
HTM, less than 12 months, fair value	45	218
HTM, Less than 12 months, gross unrealized losses	1	3
HTM, 12 months or longer, fair value	2,214	2,172
HTM, 12 months or longer, gross unrealized losses	126	64
Privately issued
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	31	34
HTM, 12 months or longer, gross unrealized losses	$ 5	$ 5