Condensed Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Consolidated Statements of Comprehensive Income (Loss)
Gains / (loss) on cash-flow hedges, net of income tax effect	$ 6	$ 6	$ 19
Amount of losses on cash-flow hedges reclassified to earnings, net of income tax effect of	(2)	(16)	(14)
Actuarial gain (loss) on pension and other postretirement obligations, settlements and plan amendments, net of income tax effect	(2)	$ 4	$ (5)
(Gains) losses related to pension and other postretirement obligations reclassified to earnings, net of income tax effect	1
Unrealized gains on investments, net of income tax effect	$ (1)