Investment Securities - Investment Securities in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	$ 747	$ 460
AFS, less than 12 months, gross unrealized losses	2	4
AFS, 12 months or longer, fair value	5,021	9,917
AFS, 12 months or longer, gross unrealized losses	106	247
Total investment securities, less than 12 months, fair value	773	2,011
Total investment securities, less than 12 months, gross unrealized losses	2	27
Total investment securities, 12 months or longer, fair value	17,468	21,761
Total investment securities, 12 months or longer, gross unrealized losses	921	1,259
Schedule of Held-to-Maturity Securities [Line Items]
HTM, less than 12 months, fair value	26	1,551
HTM, Less than 12 months, gross unrealized losses	0	23
HTM, 12 months or longer, fair value	12,447	11,844
HTM, 12 months or longer, gross unrealized losses	815	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	125	229
AFS, less than 12 months, gross unrealized losses	0	1
AFS, 12 months or longer, fair value	3,069	7,474
AFS, 12 months or longer, gross unrealized losses	26	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	949	924
HTM, 12 months or longer, gross unrealized losses	14	31
Commercial
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	395	74
AFS, less than 12 months, gross unrealized losses	2	1
AFS, 12 months or longer, fair value	128	330
AFS, 12 months or longer, gross unrealized losses	1	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	1,957	1,575
HTM, 12 months or longer, gross unrealized losses	81	121
Residential
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	227	151
AFS, less than 12 months, gross unrealized losses	0	2
AFS, 12 months or longer, fair value	1,760	1,959
AFS, 12 months or longer, gross unrealized losses	77	116
Schedule of Held-to-Maturity Securities [Line Items]
HTM, less than 12 months, fair value	0	955
HTM, Less than 12 months, gross unrealized losses	0	11
HTM, 12 months or longer, fair value	7,318	7,139
HTM, 12 months or longer, gross unrealized losses	646	791
Other debt securities
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract]
AFS, less than 12 months, fair value	0	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	26	218
HTM, Less than 12 months, gross unrealized losses	0	3
HTM, 12 months or longer, fair value	2,192	2,172
HTM, 12 months or longer, gross unrealized losses	71	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	$ 3	$ 5