Fair Value Measurements and Derivatives - Deferred Gain (Loss) in AOCI on Cash Flow Hedging Relationships (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Foreign Currency Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months	$ 3
Forward Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Foreign Currency Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months	3
Currency Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Foreign Currency Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months	0
Cash Flow Hedging [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
AOCI before Tax	(53)	$ (58)
Cash Flow Hedging [Member] | Forward Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
AOCI before Tax	3	2
Cash Flow Hedging [Member] | Currency Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
AOCI before Tax	$ (56)	$ (60)