ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Schedule of Pretax and After-tax Components of Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI activity before reclassification, net amount			$ 329	$ (165)
Amounts reclassified from AOCI to earnings, net amount			3	20
Other comprehensive income (loss) on securities available for sale, gross amount	$ 611	$ (146)	450	(197)
Other comprehensive loss on securities available for sale, tax	(160)	38	(118)	52
Other comprehensive income (loss), net of tax	451	(108)	332	(145)
Realized (gain) loss on sale of investment securities, net	0	12	0	26
Provision for credit losses	0	(3)	0	0
Unrealized loss on securities available for sale:
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI activity before reclassification, gross amount	594	(155)	440	(229)
AOCI activity before reclassification, tax	(156)	40	(115)	60
AOCI activity before reclassification, net amount	438	(115)	325	(169)
Amounts reclassified from AOCI to earnings, gross amount	0	9	0	26
Amounts reclassified from AOCI to earnings, tax	0	(2)	0	(7)
Amounts reclassified from AOCI to earnings, net amount	0	7	0	19
Other comprehensive income (loss) on securities available for sale, gross amount	594	(146)	440	(203)
Other comprehensive loss on securities available for sale, tax	(156)	38	(115)	53
Other comprehensive income (loss), net of tax	438	(108)	325	(150)
Unrealized loss on securities available for sale transferred to held to maturity
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI activity before reclassification, net amount			0	0
Amounts reclassified from AOCI to earnings, gross amount	1	0	1	1
Amounts reclassified from AOCI to earnings, tax	0	0	0	0
Amounts reclassified from AOCI to earnings, net amount	1	0	1	1
Other comprehensive income (loss) on securities available for sale, gross amount	1	0	1	1
Other comprehensive loss on securities available for sale, tax	0	0	0	0
Other comprehensive income (loss), net of tax	1	0	1	1
Defined benefit pension items
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI activity before reclassification, net amount			(8)	4
Amounts reclassified from AOCI to earnings, net amount			0	0
Other comprehensive income (loss) on securities available for sale, gross amount			(10)	5
Other comprehensive loss on securities available for sale, tax			2	(1)
Other comprehensive income (loss), net of tax			(8)	4
Unrealized gain on cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI activity before reclassification, gross amount	14	0	17	0
AOCI activity before reclassification, tax	(4)	0	(5)	0
AOCI activity before reclassification, net amount	10	0	12	0
Amounts reclassified from AOCI to earnings, gross amount	2	0	2	0
Amounts reclassified from AOCI to earnings, tax	0	0	0	0
Amounts reclassified from AOCI to earnings, net amount	2	0	2	0
Other comprehensive income (loss) on securities available for sale, gross amount	16	0	19	0
Other comprehensive loss on securities available for sale, tax	(4)	0	(5)	0
Other comprehensive income (loss), net of tax	$ 12	$ 0	$ 14	$ 0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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