Shareholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 10,294
Other comprehensive (loss) income, net of tax	60	$ 90
Ending balance	10,748
AOCI Attributable to Parent [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Ending balance	(708)	(1,148)
Unrealized Gain (Loss) on Cash Flow Hedges [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	16	17
Other comprehensive (loss) income, net of tax	1	(4)
Ending balance	17	13
Defined Benefit Plans [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	1	(20)
Other comprehensive (loss) income, net of tax	0	0
Ending balance	1	(20)
Foreign Currency Translation Adjustment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(785)	(1,235)
Other comprehensive (loss) income, net of tax	59	94
Ending balance	$ (726)	$ (1,141)