Securities - Schedule of Amortized Cost and Fair Value of Securities Held to Maturity (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity, total	$ 3,463	$ 2,868
Held-to-maturity, Accumulated Unrecognized Gain	62	105
Held-to-maturity, Accumulated Unrecognized Loss	(19)	0
Held-to-maturity, Fair Value	3,506	2,973
U.S. Treasury
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity, total	1	1
Held-to-maturity, Accumulated Unrecognized Gain	0	0
Held-to-maturity, Accumulated Unrecognized Loss	0	0
Held-to-maturity, Fair Value	1	1
U.S. government agencies
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity, total	1	1
Held-to-maturity, Accumulated Unrecognized Gain	0	0
Held-to-maturity, Accumulated Unrecognized Loss	0	0
Held-to-maturity, Fair Value	1	1
U.S. government-sponsored entities
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity, total		120
Held-to-maturity, Accumulated Unrecognized Gain		1
Held-to-maturity, Accumulated Unrecognized Loss		0
Held-to-maturity, Fair Value		121
Agency mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity, total	1,191	769
Held-to-maturity, Accumulated Unrecognized Gain	15	29
Held-to-maturity, Accumulated Unrecognized Loss	(5)	0
Held-to-maturity, Fair Value	1,201	798
Agency collateralized mortgage obligations
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity, total	930	562
Held-to-maturity, Accumulated Unrecognized Gain	5	17
Held-to-maturity, Accumulated Unrecognized Loss	(12)	0
Held-to-maturity, Fair Value	923	579
Commercial mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity, total	323	307
Held-to-maturity, Accumulated Unrecognized Gain	3	10
Held-to-maturity, Accumulated Unrecognized Loss	(2)	0
Held-to-maturity, Fair Value	324	317
States of the U.S. and political subdivisions (municipals)
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity, total	1,017	1,108
Held-to-maturity, Accumulated Unrecognized Gain	39	48
Held-to-maturity, Accumulated Unrecognized Loss	0	0
Held-to-maturity, Fair Value	$ 1,056	$ 1,156