Shareholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	$ 11,659	$ 10,294
Other comprehensive (loss) income, net of tax	42	60
Balance at end of period	11,984	10,748
AOCI Attributable to Parent [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	(1,066)	(768)
Balance at end of period	(1,024)	(708)
Unrealized Gain (Loss) on Hedges [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	9	16
Other comprehensive (loss) income, net of tax	(15)	1
Balance at end of period	(6)	17
Defined Benefit Plans [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	1	1
Other comprehensive (loss) income, net of tax	0	0
Balance at end of period	1	1
Foreign Currency Translation Adjustment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	(1,076)	(785)
Other comprehensive (loss) income, net of tax	57	59
Balance at end of period	$ (1,019)	$ (726)