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, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) on securities available for sale and cash flow hedges, gross amount	$ 95	$ 611	$ 540	$ 450
Other comprehensive income (loss) on securities available for sale and cash flow hedges, tax	(25)	(160)	(139)	(118)
Other comprehensive income, net of tax	70	451	401	332
AOCI activity before reclassification, net amount			404	329
Amounts reclassified from AOCI to earnings, net amount			(3)	3
Unrealized loss on securities available for sale:
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) on securities available for sale and cash flow hedges, gross amount	97	594	538	440
Other comprehensive income (loss) on securities available for sale and cash flow hedges, tax	(25)	(156)	(138)	(115)
Other comprehensive income, net of tax	72	438	400	325
Unrealized loss on securities available for sale transferred to held to maturity
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income, net of tax			0	1
AOCI activity before reclassification, net amount			0	0
Amounts reclassified from AOCI to earnings, gross amount	1	1	1	1
Amounts reclassified from AOCI to earnings, tax	(1)	0	(1)	0
Amounts reclassified from AOCI to earnings, net amount	0	1	0	1
Defined benefit pension items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) on securities available for sale and cash flow hedges, gross amount	(1)	0	(5)	(10)
Other comprehensive income (loss) on securities available for sale and cash flow hedges, tax	0	0	1	2
Other comprehensive income, net of tax	(1)	0	(4)	(8)
AOCI activity before reclassification, net amount			(4)	(8)
Amounts reclassified from AOCI to earnings, net amount			0	0
Unrealized gain on cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) on securities available for sale and cash flow hedges, gross amount	(2)	16	6	19
Other comprehensive income (loss) on securities available for sale and cash flow hedges, tax	1	(4)	(1)	(5)
Other comprehensive income, net of tax	(1)	12	5	14
AOCI activity before reclassification, gross amount	(2)	14	10	17
AOCI activity before reclassification, tax	1	(4)	(2)	(5)
AOCI activity before reclassification, net amount	(1)	10	8	12
Amounts reclassified from AOCI to earnings, gross amount	0	2	(4)	2
Amounts reclassified from AOCI to earnings, tax	0	0	1	0
Amounts reclassified from AOCI to earnings, net amount	$ 0	$ 2	$ (3)	$ 2