RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)​​ - Components of AOCI (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 24,060	$ 23,958	$ 23,845	$ 22,928	$ 22,735	$ 22,370	$ 23,845	$ 22,370
Gain (loss) in other comprehensive income (loss) before reclassifications							2
(Gain) loss reclassified from accumulated other comprehensive income (loss)							24
Other comprehensive income (loss)	8	7	11	2	5	13	26	20
Balance at end of period	23,238	24,060	23,958	23,577	22,928	22,735	23,238	23,577
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(198)	(205)	(216)	(247)	(252)	(265)	(216)	(265)
Other comprehensive income (loss)	8	7	11	2	5	13
Balance at end of period	(190)	$ (198)	(205)	$ (245)	$ (247)	$ (252)	(190)	$ (245)
Unrealized Gain (Loss) on Investment Securities, net
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			0				0
Gain (loss) in other comprehensive income (loss) before reclassifications							(1)
(Gain) loss reclassified from accumulated other comprehensive income (loss)							0
Other comprehensive income (loss)							(1)
Balance at end of period	(1)						(1)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			117				117
Gain (loss) in other comprehensive income (loss) before reclassifications							3
(Gain) loss reclassified from accumulated other comprehensive income (loss)							0
Other comprehensive income (loss)							3
Balance at end of period	120						120
Pension and Other Post-retirement Benefit Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(237)				(237)
Gain (loss) in other comprehensive income (loss) before reclassifications							(1)
(Gain) loss reclassified from accumulated other comprehensive income (loss)							18
Other comprehensive income (loss)							17
Balance at end of period	(220)						(220)
Unrealized Gain (Loss) on Cash flow Hedge Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			$ (96)				(96)
Gain (loss) in other comprehensive income (loss) before reclassifications							1
(Gain) loss reclassified from accumulated other comprehensive income (loss)							6
Other comprehensive income (loss)							7
Balance at end of period	$ (89)						$ (89)