Derivative instruments (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
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	$ (25)	$ (79)
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	100	(87)
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	$ (125)	$ 8