ACCUMULATED OTHER COMPREHENSIVE LOSS (Accumulated Other Comprehensive Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (1,665)	$ (1,561)
Net other comprehensive income	(105)	(104)	$ 45
Ending balance	(1,770)	(1,665)	(1,561)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(56)	(57)	(59)
Other comprehensive income (loss) before reclassifications	0	1	2
Net other comprehensive income	1	1	2
Ending balance	(55)	(56)	(57)
Pension and Other Postretirement Benefits
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,609)	(1,504)	(1,293)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(242)	(213)	(29)
Other Comprehensive Income (Loss) before Reclassifications, Tax	57	51	7
Other comprehensive income (loss) before reclassifications	(185)	(162)	(22)
Amounts reclassified from AOCL	79	57	65
Reclassification from AOCI, Current Period, Tax	(24)	(18)	(20)
Net other comprehensive income	(106)	(105)	43
Ending balance	(1,715)	(1,609)	(1,504)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Amounts reclassified from AOCL	1	0	0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension and Other Postretirement Benefits
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	103	75	85
Retained Earnings [Member] | Pension and Other Postretirement Benefits
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of stranded tax effects	$ 0	$ 0	$ (254)