Shareholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			$ 10,294
Other comprehensive (loss) income, net of tax	$ (228)	$ 96	(168)	$ 186
Ending balance	10,976		10,976
AOCI Attributable to Parent [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Ending balance	(936)	(1,052)	(936)	(1,052)
Unrealized Gain (Loss) on Cash Flow Hedges [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	17	13	16	17
Other comprehensive (loss) income, net of tax	17	(7)	18	(11)
Ending balance	34	6	34	6
Defined Benefit Plans [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	1	(20)	1	(20)
Other comprehensive (loss) income, net of tax	0	(1)	0	(1)
Ending balance	1	(21)	1	(21)
Foreign Currency Translation Adjustment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(726)	(1,141)	(785)	(1,235)
Other comprehensive (loss) income, net of tax	(245)	104	(186)	198
Ending balance	$ (971)	$ (1,037)	$ (971)	$ (1,037)