Changes in Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	$ 10	$ 111	$ 79	$ 28
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(19)	2	(34)	15
Total other comprehensive income (loss)	(9)	112	45	42
Accumulated Other Comprehensive Income (Loss), Net of Tax	78	(16)	78	(16)	$ 87	$ 33	$ (128)	$ (59)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	8	(40)	22	(31)
Gain (Loss) on Derivative Used in Net Investment Hedge, after Tax	(8)	(5)	(16)	(5)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	0	(45)	7	(36)
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	(46)	(68)	(46)	(68)	(46)	(53)	(22)	(32)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax	2	151	58	59
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(11)	7	(18)	19
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, Net of Tax	0	0	0	1
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax	(9)	158	40	78
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Reclassification Adjustments and Tax	0	0	0	0
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	150	79	150	79	160	111	(79)	1
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	0	0	0	0
Accumulated Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax	0	0	0	0	0	0	0	(1)
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	0	0	1	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	0	0	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	0	0	1	0
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	$ (26)	$ (27)	$ (26)	$ (27)	$ (26)	$ (25)	$ (27)	$ (27)