Financial Instruments - Derivatives and hedging (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Assets, fair value	$ 74	$ 150
Liabilities, fair value	(82)	(95)
Currency exchange contracts | Designated as hedging instrument
Derivatives, Fair Value [Line Items]
Assets, fair value	0	6
Liabilities, fair value	(7)	0
Currency exchange contracts | Not designated as hedging instrument
Derivatives, Fair Value [Line Items]
Assets, fair value	74	144
Liabilities, fair value	$ (75)	$ (95)