Shareholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			$ 10,294
Other comprehensive (loss) income, net of tax	$ (34)	$ 117	(202)	$ 303
Ending balance	11,852		11,852
AOCI Attributable to Parent [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Ending balance	(970)	(935)	(970)	(935)
Unrealized Gain (Loss) on Cash Flow Hedges [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	34	6	16	17
Other comprehensive (loss) income, net of tax	1	(3)	19	(14)
Ending balance	35	3	35	3
Defined Benefit Plans [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	1	(21)	1	(20)
Other comprehensive (loss) income, net of tax	0	0	0	(1)
Ending balance	1	(21)	1	(21)
Foreign Currency Translation Adjustment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(971)	(1,037)	(785)	(1,235)
Other comprehensive (loss) income, net of tax	(35)	120	(221)	318
Ending balance	$ (1,006)	$ (917)	$ (1,006)	$ (917)