INVESTMENT SECURITIES - Schedule of Fair Values and Unrealized Losses of Impaired Securities, by Length of Impairment (Details) $ in Millions	Sep. 30, 2026 USD ($) security	Dec. 31, 2025 USD ($) security
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	113	12
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	187	203
Debt securities, available-for-sale, number of positions \| security	300	215
Debt securities, available-for-sale, less than 12 months, fair value	$ 2,559	$ 251
Debt securities, available-for-sale, 12 months or longer, fair value	982	1,322
Debt securities, available-for-sale, fair value	3,541	1,573
Debt securities, available-for-sale, less than 12 months, unrealized losses	(79)	(1)
Debt securities, available-for-sale, 12 months or longer, unrealized losses	(102)	(84)
Debt securities, available-for-sale, unrealized losses	$ (181)	$ (85)
U.S. Treasury
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, fair value	$ 323
Debt securities, available-for-sale, 12 months or longer, fair value	0
Debt securities, available-for-sale, fair value	323
Debt securities, available-for-sale, less than 12 months, unrealized losses	(6)
Debt securities, available-for-sale, 12 months or longer, unrealized losses	0
Debt securities, available-for-sale, unrealized losses	$ (6)
U.S. government agencies
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	3	5
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	11	12
Debt securities, available-for-sale, number of positions \| security	14	17
Debt securities, available-for-sale, less than 12 months, fair value	$ 3	$ 8
Debt securities, available-for-sale, 12 months or longer, fair value	13	20
Debt securities, available-for-sale, fair value	16	28
Debt securities, available-for-sale, less than 12 months, unrealized losses	0	0
Debt securities, available-for-sale, 12 months or longer, unrealized losses	0	0
Debt securities, available-for-sale, unrealized losses	$ 0	$ 0
U.S. GSE
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	11	2
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	0	3
Debt securities, available-for-sale, number of positions \| security	11	5
Debt securities, available-for-sale, less than 12 months, fair value	$ 280	$ 65
Debt securities, available-for-sale, 12 months or longer, fair value	0	51
Debt securities, available-for-sale, fair value	280	116
Debt securities, available-for-sale, less than 12 months, unrealized losses	(10)	0
Debt securities, available-for-sale, 12 months or longer, unrealized losses	0	0
Debt securities, available-for-sale, unrealized losses	$ (10)	$ 0
Agency MBS
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	25	1
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	86	90
Debt securities, available-for-sale, number of positions \| security	111	91
Debt securities, available-for-sale, less than 12 months, fair value	$ 547	$ 46
Debt securities, available-for-sale, 12 months or longer, fair value	160	251
Debt securities, available-for-sale, fair value	707	297
Debt securities, available-for-sale, less than 12 months, unrealized losses	(26)	0
Debt securities, available-for-sale, 12 months or longer, unrealized losses	(10)	(8)
Debt securities, available-for-sale, unrealized losses	$ (36)	$ (8)
Agency CMO
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	64	64
Debt securities, available-for-sale, number of positions \| security	64	64
Debt securities, available-for-sale, less than 12 months, fair value	$ 0	$ 0
Debt securities, available-for-sale, 12 months or longer, fair value	494	601
Debt securities, available-for-sale, fair value	494	601
Debt securities, available-for-sale, less than 12 months, unrealized losses	0	0
Debt securities, available-for-sale, 12 months or longer, unrealized losses	(76)	(61)
Debt securities, available-for-sale, unrealized losses	$ (76)	$ (61)
Agency commercial MBS
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	48	4
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	19	22
Debt securities, available-for-sale, number of positions \| security	67	26
Debt securities, available-for-sale, less than 12 months, fair value	$ 1,344	$ 132
Debt securities, available-for-sale, 12 months or longer, fair value	303	371
Debt securities, available-for-sale, fair value	1,647	503
Debt securities, available-for-sale, less than 12 months, unrealized losses	(35)	(1)
Debt securities, available-for-sale, 12 months or longer, unrealized losses	(15)	(14)
Debt securities, available-for-sale, unrealized losses	$ (50)	$ (15)
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	0	0
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	6	9
Debt securities, available-for-sale, number of positions \| security	6	9
Debt securities, available-for-sale, less than 12 months, fair value	$ 0	$ 0
Debt securities, available-for-sale, 12 months or longer, fair value	10	19
Debt securities, available-for-sale, fair value	10	19
Debt securities, available-for-sale, less than 12 months, unrealized losses	0	0
Debt securities, available-for-sale, 12 months or longer, unrealized losses	(1)	(1)
Debt securities, available-for-sale, unrealized losses	$ (1)	$ (1)
Other debt securities
Schedule Of Securities [Line Items]
Debt securities, available-for-sale, less than 12 months, number of positions \| security	13	0
Debt securities, available-for-sale, 12 months or longer, number of positions \| security	1	3
Debt securities, available-for-sale, number of positions \| security	14	3
Debt securities, available-for-sale, less than 12 months, fair value	$ 62	$ 0
Debt securities, available-for-sale, 12 months or longer, fair value	2	9
Debt securities, available-for-sale, fair value	64	9
Debt securities, available-for-sale, less than 12 months, unrealized losses	(2)	0
Debt securities, available-for-sale, 12 months or longer, unrealized losses	0	0
Debt securities, available-for-sale, unrealized losses	$ (2)	$ 0

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