SECURITIES - Fair Values and Unrealized Losses of Impaired Securities, by Length of Impairment (Details) $ in Millions	Mar. 31, 2022 USD ($) security	Dec. 31, 2021 USD ($) security
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	210	60
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	21	14
Debt securities, available-for-sale, number of positions \| security	231	74
Debt securities, available-for-sale, less than 12 months	$ 3,006	$ 1,679
Debt securities, available-for-sale, 12 months or longer	262	102
Debt securities, available-for-sale, unrealized loss position	3,268	1,781
Debt securities, available-for-sale, less than 12 months, accumulated loss	(133)	(23)
Debt securities, available-for-sale, 12 months or longer, accumulated loss	(23)	(3)
Debt securities, available-for-sale, accumulated loss	$ (156)	$ (26)
U.S. Treasury
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	4	3
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	0	0
Debt securities, available-for-sale, number of positions \| security	4	3
Debt securities, available-for-sale, less than 12 months	$ 194	$ 151
Debt securities, available-for-sale, 12 months or longer	0	0
Debt securities, available-for-sale, unrealized loss position	194	151
Debt securities, available-for-sale, less than 12 months, accumulated loss	(11)	(1)
Debt securities, available-for-sale, 12 months or longer, accumulated loss	0	0
Debt securities, available-for-sale, accumulated loss	$ (11)	$ (1)
U.S. government agencies
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	6	3
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	9	9
Debt securities, available-for-sale, number of positions \| security	15	12
Debt securities, available-for-sale, less than 12 months	$ 50	$ 22
Debt securities, available-for-sale, 12 months or longer	7	8
Debt securities, available-for-sale, unrealized loss position	57	30
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	11	3
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	1	1
Debt securities, available-for-sale, number of positions \| security	12	4
Debt securities, available-for-sale, less than 12 months	$ 181	$ 99
Debt securities, available-for-sale, 12 months or longer	23	24
Debt securities, available-for-sale, unrealized loss position	204	123
Debt securities, available-for-sale, less than 12 months, accumulated loss	(8)	(1)
Debt securities, available-for-sale, 12 months or longer, accumulated loss	(2)	(1)
Debt securities, available-for-sale, accumulated loss	$ (10)	$ (2)
Agency mortgage-backed securities
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	101	13
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	0	0
Debt securities, available-for-sale, number of positions \| security	101	13
Debt securities, available-for-sale, less than 12 months	$ 1,346	$ 599
Debt securities, available-for-sale, 12 months or longer	0	0
Debt securities, available-for-sale, unrealized loss position	1,346	599
Debt securities, available-for-sale, less than 12 months, accumulated loss	(54)	(4)
Debt securities, available-for-sale, 12 months or longer, accumulated loss	0	0
Debt securities, available-for-sale, accumulated loss	$ (54)	$ (4)
Agency collateralized mortgage obligations
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	60	23
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	7	3
Debt securities, available-for-sale, number of positions \| security	67	26
Debt securities, available-for-sale, less than 12 months	$ 952	$ 659
Debt securities, available-for-sale, 12 months or longer	196	68
Debt securities, available-for-sale, unrealized loss position	1,148	727
Debt securities, available-for-sale, less than 12 months, accumulated loss	(49)	(15)
Debt securities, available-for-sale, 12 months or longer, accumulated loss	(18)	(2)
Debt securities, available-for-sale, accumulated loss	$ (67)	$ (17)
Commercial mortgage-backed securities
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	11	5
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	2	0
Debt securities, available-for-sale, number of positions \| security	13	5
Debt securities, available-for-sale, less than 12 months	$ 250	$ 125
Debt securities, available-for-sale, 12 months or longer	31	0
Debt securities, available-for-sale, unrealized loss position	281	125
Debt securities, available-for-sale, less than 12 months, accumulated loss	(10)	(2)
Debt securities, available-for-sale, 12 months or longer, accumulated loss	(2)	0
Debt securities, available-for-sale, accumulated loss	$ (12)	$ (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	12	10
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	1	0
Debt securities, available-for-sale, number of positions \| security	13	10
Debt securities, available-for-sale, less than 12 months	$ 27	$ 24
Debt securities, available-for-sale, 12 months or longer	3	0
Debt securities, available-for-sale, unrealized loss position	30	24
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
Other debt securities
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	5	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	6	1
Debt securities, available-for-sale, less than 12 months	$ 6	$ 0
Debt securities, available-for-sale, 12 months or longer	2	2
Debt securities, available-for-sale, unrealized loss position	8	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

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