ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Schedule of Pretax and After-tax Components of Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI activity before reclassification, net amount				$ (50)
Amounts reclassified from AOCI to earnings, net amount				13
Other comprehensive income (loss) on securities available for sale, gross amount	$ (37)	$ (139)	$ (161)	(51)
Other comprehensive loss on securities available for sale, tax	9	36	42	14
Other comprehensive loss, net of tax	(28)	(103)	(119)	(37)
Realized loss on sale of investment securities available for sale, net	0	0	0	14
Provision for credit losses	0	(1)	0	3
Unrealized loss on securities available for sale:
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI activity before reclassification, gross amount	(30)	(134)	(154)	(74)
AOCI activity before reclassification, tax	8	35	41	20
AOCI activity before reclassification, net amount	(22)	(99)	(113)	(54)
Amounts reclassified from AOCI to earnings, gross amount	0	(1)	0	17
Amounts reclassified from AOCI to earnings, tax	0	0	0	(5)
Amounts reclassified from AOCI to earnings, net amount	0	(1)	0	12
Other comprehensive income (loss) on securities available for sale, gross amount	(30)	(135)	(154)	(57)
Other comprehensive loss on securities available for sale, tax	8	35	41	15
Other comprehensive loss, net of tax	(22)	(100)	(113)	(42)
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
Amounts reclassified from AOCI to earnings, gross amount	0	1	0	1
Amounts reclassified from AOCI to earnings, tax	0	0	0	0
Amounts reclassified from AOCI to earnings, net amount	0	1	0	1
Other comprehensive income (loss) on securities available for sale, gross amount	0	1	0	1
Other comprehensive loss on securities available for sale, tax	0	0	0	0
Other comprehensive loss, net of tax	0	1	0	1
Defined benefit pension items
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI activity before reclassification, net amount				4
Amounts reclassified from AOCI to earnings, net amount				0
Other comprehensive income (loss) on securities available for sale, gross amount	(10)	(5)	(10)	5
Other comprehensive loss on securities available for sale, tax	2	1	2	(1)
Other comprehensive loss, net of tax	(8)	(4)	(8)	4
Unrealized gain on cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI activity before reclassification, net amount				0
Amounts reclassified from AOCI to earnings, net amount				0
Other comprehensive income (loss) on securities available for sale, gross amount	3	0	3	0
Other comprehensive loss on securities available for sale, tax	(1)	0	(1)	0
Other comprehensive loss, net of tax	$ 2	$ 0	$ 2	$ 0