ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME - Schedule of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax	$ (187)	$ (637)
Income Taxes	28	146
Net of Income Taxes	(159)	(491)
Unrealized loss on securities available for sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax	(312)	(752)
Income Taxes	60	175
Net of Income Taxes	(252)	(577)
Unrealized loss on securities available for sale transferred to held to maturity
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax	(6)	(7)
Income Taxes	2	2
Net of Income Taxes	(4)	(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	19	0
Income Taxes	(5)	0
Net of Income Taxes	$ 14	$ 0