CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (1,733)	$ 1,389	$ 626
Items related to employee benefit plans:
Change in net actuarial gain (loss), net of ($45), $(60) and $113 tax	133	83	(168)
Change in net prior service credit, net of $(3), $(4) and $(4) tax	9	8	6
Foreign currency translation adjustment and other, net of $50, $(17) and $— tax	(201)	31	(21)
Net current-period other comprehensive income (loss)	(59)	122	(183)
COMPREHENSIVE (LOSS) INCOME	$ (1,792)	$ 1,511	$ 443