Changes in Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	$ (68)	$ (58)	$ (68)	$ (58)	$ (22)	$ (32)	$ (71)	$ (79)
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	79	31	79	31	(79)	1	52	107
Accumulated Other Comprehensive Income (Loss), Debt Securities, Available-for-sale, Adjustment, after Tax	0	(4)	0	(4)		(1)	(6)	(6)
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	(27)	(22)	(27)	(22)	(27)	(27)	(21)	(21)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(16)	(53)	(16)	(53)	$ (128)	$ (59)	$ (46)	$ 1
Cumulative Translation Adjustment, Net of Tax, Period Increase (Decrease)	(40)	13	(31)	21
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Before Reclassifications, Net of Tax	151	(4)	59	(41)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Reclassification Adjustments, after Tax		0	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	0	0	0	(2)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	111	9	28	(22)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(5)	0	(5)	0
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Reclassified from OCI, Net of Tax	7	(17)	19	(35)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax		2	1	2
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	0	(1)	0	1
Other Comprehensive Income (Loss), Reclassifications out of OCI, Net of Tax	2	(16)	15	(32)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(45)	13	(36)	21
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	158	(21)	78	(76)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Reclassification Adjustments and Tax	0	2	0	2
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	0	(1)	0	(1)
Other Comprehensive Income (Loss), Net of Tax	$ 112	$ (7)	$ 42	$ (54)