Derivative instruments (Locations and Gain (Loss) for Derivatives Not Designated as Hedging Instruments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Foreign currency contracts [Member] | Interest And Other Income [Member]
Location in the Condensed Consolidated Statements of Income and the amount of gain (loss) recognized in earnings for our derivative instruments not designated as hedging instruments
Amount of gain (loss) recognized in interest and other income, net	$ (2)	$ 1	$ 12	$ (33)