Derivative instruments (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 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	$ 53	$ 147	$ 28	$ 68
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	21	189	121	102
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	32	(35)	(93)	(27)
Forward interest rate 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	$ 0	$ (7)	$ 0	$ (7)