Derivative instruments (Details) (Derivatives in cash flow hedging relationships [Member], USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Effective portion of the unrealized gain/(loss) recognized in Other Comprehensive Income for our cash flow hedge contracts
Unrealized gain (loss) on derivative instruments recognized in Other Comprehensive Income, effective portion, net	$ (21)	$ 224	$ (218)	$ 399
Forward interest rate contracts [Member]
Effective portion of the unrealized gain/(loss) recognized in Other Comprehensive Income for our cash flow hedge contracts
Unrealized gain (loss) on derivative instruments recognized in Other Comprehensive Income, effective portion, net	0	0	0	0
Foreign currency contracts [Member]
Effective portion of the unrealized gain/(loss) recognized in Other Comprehensive Income for our cash flow hedge contracts
Unrealized gain (loss) on derivative instruments recognized in Other Comprehensive Income, effective portion, net	$ (21)	$ 224	$ (218)	$ 399