ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Schedule of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax	$ (798)	$ (637)
Income Taxes	188	146
Net of Income Taxes	(610)	(491)
Unrealized loss on securities available for sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax	(906)	(752)
Income Taxes	216	175
Net of Income Taxes	(690)	(577)
Unrealized loss on securities available for sale transferred to held to maturity
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax	(7)	(7)
Income Taxes	2	2
Net of Income Taxes	(5)	(5)
Defined benefit pension items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax	112	122
Income Taxes	(29)	(31)
Net of Income Taxes	83	91
Unrealized gain on cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax	3	0
Income Taxes	(1)	0
Net of Income Taxes	$ 2	$ 0