Fair Value Measurements Fair Value Measurements - Accumulated Other Comprehensive Income/Loss (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (77)	$ (37)	$ 4	$ 15	$ (77)	$ 4	$ (24)	$ 6
Other comprehensive income/(loss) before reclassifications	(41)	(13)	(11)	9
Amounts reclassified from accumulated other comprehensive loss	1		0		1	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(5)		(22)		(5)	(19)
Other Comprehensive Income (Loss), Net of Tax	(40)	(15)	(13)		(55)	(5)
Designated as Hedging Instrument [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	(65)	(30)	13	4	(65)	13	(13)	0
Other comprehensive income/(loss) before reclassifications	(36)	(17)	9	4
Amounts reclassified from accumulated other comprehensive loss	1
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	(35)	(17)	9	4
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	(12)	(7)	(7)	10	(12)	(7)	(9)	9
Other comprehensive income/(loss) before reclassifications	(5)	2	(17)	1
Amounts reclassified from accumulated other comprehensive loss	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(5)	2	(17)	1
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	0	0	(2)	1	$ 0	$ (2)	$ (2)	$ (3)
Other comprehensive income/(loss) before reclassifications	0	2	(3)	4
Amounts reclassified from accumulated other comprehensive loss	0
Other Comprehensive Income, Other, Net of Tax	0	2	(3)	4
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Net of Tax	$ (40)	$ (13)	$ (11)	$ 9