CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 1,389	$ 626	$ 878
Items related to employee benefit plans:
Change in net actuarial gain (loss), net of $(60), $113 and $(12) tax	83	(168)	21
Change in net prior service credit, net of $(4), $(4) and $(47) tax	8	6	76
Foreign currency translation adjustment and other, net of $(17), $— and $— tax	31	(21)	(14)
Net current-period other comprehensive income (loss)	122	(183)	83
COMPREHENSIVE INCOME	$ 1,511	$ 443	$ 961