OTHER COMPREHENSIVE INCOME (LOSS) - Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 5,150	$ 4,959
Other comprehensive (loss) income before reclassifications	(142)
Amounts reclassified from AOCI	2
Other Comprehensive Income (Loss)	(140)	(12)
Balance at end of period	5,439	4,974
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	(128)
Amounts reclassified from AOCI	0
Other Comprehensive Income (Loss)	(128)
Balance at end of period	(120)
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	(15)
Amounts reclassified from AOCI	2
Other Comprehensive Income (Loss)	(13)
Balance at end of period	(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)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(62)	(39)
Balance at end of period	$ (202)	$ (51)