Securities - Summaries of Fair Values and Unrealized Losses of Securities, Segregated by Length of Impairment (Detail) $ in Millions	Dec. 31, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	60	7
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	14	17
Debt securities, available-for-sale, number of positions \| security	74	24
Debt securities, available-for-sale, less than 12 months	$ 1,679	$ 168
Debt securities, available-for-sale, 12 months or longer	102	71
Debt securities, available-for-sale, unrealized loss position	1,781	239
Debt securities, available-for-sale, less than 12 months, accumulated loss	(23)	(1)
Debt securities, available-for-sale, 12 months or longer, accumulated loss	(3)	0
Debt securities, available-for-sale, accumulated loss	$ (26)	$ (1)
U.S. Treasury
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	3
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	0
Debt securities, available-for-sale, number of positions \| security	3
Debt securities, available-for-sale, less than 12 months	$ 151
Debt securities, available-for-sale, 12 months or longer	0
Debt securities, available-for-sale, unrealized loss position	151
Debt securities, available-for-sale, less than 12 months, accumulated loss	(1)
Debt securities, available-for-sale, 12 months or longer, accumulated loss	0
Debt securities, available-for-sale, accumulated loss	$ (1)
U.S. government agencies
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	3	1
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	9	16
Debt securities, available-for-sale, number of positions \| security	12	17
Debt securities, available-for-sale, less than 12 months	$ 22	$ 13
Debt securities, available-for-sale, 12 months or longer	8	69
Debt securities, available-for-sale, unrealized loss position	30	82
Debt securities, available-for-sale, less than 12 months, accumulated loss	0	0
Debt securities, available-for-sale, 12 months or longer, accumulated loss	0	0
Debt securities, available-for-sale, accumulated loss	$ 0	$ 0
U.S. government-sponsored entities
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	3	1
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	1	0
Debt securities, available-for-sale, number of positions \| security	4	1
Debt securities, available-for-sale, less than 12 months	$ 99	$ 25
Debt securities, available-for-sale, 12 months or longer	24	0
Debt securities, available-for-sale, unrealized loss position	123	25
Debt securities, available-for-sale, less than 12 months, accumulated loss	(1)	0
Debt securities, available-for-sale, 12 months or longer, accumulated loss	(1)	0
Debt securities, available-for-sale, accumulated loss	$ (2)	$ 0
Agency mortgage-backed securities
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	13
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	0
Debt securities, available-for-sale, number of positions \| security	13
Debt securities, available-for-sale, less than 12 months	$ 599
Debt securities, available-for-sale, 12 months or longer	0
Debt securities, available-for-sale, unrealized loss position	599
Debt securities, available-for-sale, less than 12 months, accumulated loss	(4)
Debt securities, available-for-sale, 12 months or longer, accumulated loss	0
Debt securities, available-for-sale, accumulated loss	$ (4)
Agency collateralized mortgage obligations
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	23	5
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	3	0
Debt securities, available-for-sale, number of positions \| security	26	5
Debt securities, available-for-sale, less than 12 months	$ 659	$ 130
Debt securities, available-for-sale, 12 months or longer	68	0
Debt securities, available-for-sale, unrealized loss position	727	130
Debt securities, available-for-sale, less than 12 months, accumulated loss	(15)	(1)
Debt securities, available-for-sale, 12 months or longer, accumulated loss	(2)	0
Debt securities, available-for-sale, accumulated loss	$ (17)	$ (1)
Commercial mortgage-backed securities
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	5
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	0
Debt securities, available-for-sale, number of positions \| security	5
Debt securities, available-for-sale, less than 12 months	$ 125
Debt securities, available-for-sale, 12 months or longer	0
Debt securities, available-for-sale, unrealized loss position	125
Debt securities, available-for-sale, less than 12 months, accumulated loss	(2)
Debt securities, available-for-sale, 12 months or longer, accumulated loss	0
Debt securities, available-for-sale, accumulated loss	$ (2)
States of the U.S. and political subdivisions (municipals)
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	10
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	0
Debt securities, available-for-sale, number of positions \| security	10
Debt securities, available-for-sale, less than 12 months	$ 24
Debt securities, available-for-sale, 12 months or longer	0
Debt securities, available-for-sale, unrealized loss position	24
Debt securities, available-for-sale, less than 12 months, accumulated loss	0
Debt securities, available-for-sale, 12 months or longer, accumulated loss	0
Debt securities, available-for-sale, accumulated loss	$ 0
Other debt securities
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	0	0
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	1	1
Debt securities, available-for-sale, number of positions \| security	1	1
Debt securities, available-for-sale, less than 12 months	$ 0	$ 0
Debt securities, available-for-sale, 12 months or longer	2	2
Debt securities, available-for-sale, unrealized loss position	2	2
Debt securities, available-for-sale, less than 12 months, accumulated loss	0	0
Debt securities, available-for-sale, 12 months or longer, accumulated loss	0	0
Debt securities, available-for-sale, accumulated loss	$ 0	$ 0

Schedule Of Securities [Line Items]

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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