OTHER COMPREHENSIVE INCOME (LOSS) - Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 5,818	$ 5,436	$ 5,653	$ 5,150
Other comprehensive (loss) income before reclassifications			(38)
Amounts reclassified from AOCI			13
Other Comprehensive Income (Loss)	(27)	(126)	(25)	(316)
Balance at end of period	5,894	5,406	5,894	5,406
Unrealized Net Gains (Losses) on Debt Securities Available for Sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(269)
Other comprehensive (loss) income before reclassifications			(22)
Amounts reclassified from AOCI			0
Other Comprehensive Income (Loss)			(22)
Balance at end of period	(291)		(291)
Unrealized Net Gains (Losses) on Derivative Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(44)
Other comprehensive (loss) income before reclassifications			(17)
Amounts reclassified from AOCI			13
Other Comprehensive Income (Loss)			(4)
Balance at end of period	(48)		(48)
Unrecognized Pension and Postretirement Obligations
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(44)
Other comprehensive (loss) income before reclassifications			1
Amounts reclassified from AOCI			0
Other Comprehensive Income (Loss)			1
Balance at end of period	(43)		(43)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(355)	(252)	(357)	(62)
Balance at end of period	$ (382)	$ (378)	$ (382)	$ (378)