Changes in Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	$ 47	$ 10	$ 76	$ (12)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(7)	(8)	8	(40)
Total other comprehensive income (loss)	40	2	82	(52)
Accumulated Other Comprehensive Income (Loss), Net of Tax	25	(51)	25	(51)	$ (16)	$ (59)	$ (53)	$ 1
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	2	25	(29)	46
Gain (Loss) on Derivative Used in Net Investment Hedge, after Tax	(8)	0	(13)	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(6)	25	(42)	46
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	(74)	(33)	(74)	(33)	(68)	(32)	(58)	(79)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax	45	(15)	105	(56)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	1	(9)	20	(44)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, Net of Tax	0	1	1	3
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax	47	(24)	125	(100)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Reclassification Adjustments and Tax	0	(1)	0	(3)
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	126	7	126	7	79	1	31	107
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	(3)	0	(3)	0	(1)	(4)	(6)
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	0	0	0	(2)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	0	0	0	1
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	0	0	0	(1)
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	$ (27)	$ (22)	$ (27)	$ (22)	$ (27)	$ (27)	$ (22)	$ (21)