Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	$ 8,693
Other comprehensive loss, net of tax	470	$ (134)	$ (671)
Balance at end of period	10,294	8,693
AOCI Attributable to Parent [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	(1,238)	(1,104)	(433)
Balance at end of period	(768)	(1,238)	(1,104)
Unrealized Gain from Cash Flow Hedges [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	17	0	0
Other comprehensive loss, net of tax	(1)	17	0
Balance at end of period	16	17	0
Defined Benefit Plans [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	(20)	(13)	(11)
Other comprehensive loss, net of tax	0	(7)	(2)
Reclassification adjustment	21	0	0
Balance at end of period	1	(20)	(13)
Foreign Currency Translation Adjustment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	(1,235)	(1,091)	(422)
Other comprehensive loss, net of tax	253	(144)	(669)
Reclassification adjustment	197	0	0
Balance at end of period	$ (785)	$ (1,235)	$ (1,091)