ACCUMULATED OTHER COMPREHENSIVE INCOME- Components of AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	$ 7,237	$ 6,975	$ 6,814
Other comprehensive income before reclassifications			(2)
Amounts reclassified from AOCI	(13)	(33)	(27)
Other comprehensive loss	(13)	(33)	(29)
Income tax benefits on other comprehensive loss	(3)	(8)	(8)
Other comprehensive loss, net of tax	(10)	(25)	(21)
Ending Balance	8,675	7,237	6,975
Accumulated Other Comprehensive Income
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(5)	20	41
Other comprehensive loss, net of tax	(10)	(25)	(21)
Ending Balance	(15)	(5)	20
Gains & Losses on Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(8)	(9)	(11)
Other comprehensive income before reclassifications			0
Amounts reclassified from AOCI	1	1	2
Other comprehensive loss	1	1	2
Income tax benefits on other comprehensive loss	0	0	0
Other comprehensive loss, net of tax	1	1	2
Ending Balance	(7)	(8)	(9)
Defined Benefit Pension & OPEB Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	3	29	52
Other comprehensive income before reclassifications			(2)
Amounts reclassified from AOCI	(14)	(34)	(29)
Other comprehensive loss	(14)	(34)	(31)
Income tax benefits on other comprehensive loss	(3)	(8)	(8)
Other comprehensive loss, net of tax	(11)	(26)	(23)
Ending Balance	$ (8)	$ 3	$ 29