Derivative instruments (Effective Portion of Unrealized Gain (Loss)) (Details) - Cash flow hedge [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Effective portion of the unrealized gain (loss) recognized in Other Comprehensive Income for our derivative instruments designated as cash flow hedges
Unrealized gain (loss) on derivative instruments recognized in Other Comprehensive Income, effective portion, net	$ 149	$ 17
Foreign currency contracts [Member]
Effective portion of the unrealized gain (loss) recognized in Other Comprehensive Income for our derivative instruments designated as cash flow hedges
Unrealized gain (loss) on derivative instruments recognized in Other Comprehensive Income, effective portion, net	(89)	(47)
Cross-currency swap contracts [Member]
Effective portion of the unrealized gain (loss) recognized in Other Comprehensive Income for our derivative instruments designated as cash flow hedges
Unrealized gain (loss) on derivative instruments recognized in Other Comprehensive Income, effective portion, net	$ 238	$ 64