OTHER COMPREHENSIVE INCOME (LOSS) - Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 5,439	$ 4,974	$ 5,150	$ 4,959
Other comprehensive (loss) income before reclassifications			(194)
Amounts reclassified from AOCI			4
Other Comprehensive Income (Loss)	(50)	5	(190)	(7)
Balance at end of period	5,436	5,037	5,436	5,037
Unrealized Net Gains (Losses) on Debt Securities Available for Sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			8
Other comprehensive (loss) income before reclassifications			(178)
Amounts reclassified from AOCI			0
Other Comprehensive Income (Loss)			(178)
Balance at end of period	(170)		(170)
Unrealized Net Gains (Losses) on Derivative Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(22)
Other comprehensive (loss) income before reclassifications			(17)
Amounts reclassified from AOCI			4
Other Comprehensive Income (Loss)			(13)
Balance at end of period	(35)		(35)
Unrecognized Pension and Postretirement Obligations
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(48)
Other comprehensive (loss) income before reclassifications			1
Amounts reclassified from AOCI			0
Other Comprehensive Income (Loss)			1
Balance at end of period	(47)		(47)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(202)	(51)	(62)	(39)
Balance at end of period	$ (252)	$ (46)	$ (252)	$ (46)