Shareholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	$ 10,294	$ 8,693	$ 8,052
Other comprehensive (loss) income, net of tax	(298)	470	(134)
Balance at end of period	11,659	10,294	8,693
AOCI Attributable to Parent [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	(768)	(1,238)	(1,104)
Reclassification adjustment	82	(87)	33
Balance at end of period	(1,066)	(768)	(1,238)
Unrealized Gain Hedges [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	16	17	0
Other comprehensive (loss) income, net of tax	(7)	(1)	17
Balance at end of period	9	16	17
Defined Benefit Plans [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	1	(20)	(13)
Other comprehensive (loss) income, net of tax	0	0	(7)
Reclassification adjustment	0	21	0
Balance at end of period	1	1	(20)
Foreign Currency Translation Adjustment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	(785)	(1,235)	(1,091)
Other comprehensive (loss) income, net of tax	(291)	253	(144)
Reclassification adjustment	0	197	0
Balance at end of period	$ (1,076)	$ (785)	$ (1,235)