Derivative instruments (Details Textual) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 Net cash provided by operating activities [Member]	Sep. 30, 2011 Interest expense, net [Member]	Sep. 30, 2012 Interest expense, net [Member]	Sep. 30, 2011 Interest expense, net [Member]	Sep. 30, 2012 Foreign currency forward contracts [Member]	Dec. 31, 2011 Foreign currency forward contracts [Member]	Sep. 30, 2012 Foreign currency option contracts [Member]	Dec. 31, 2011 Foreign currency option contracts [Member]	Sep. 30, 2012 Foreign currency and cross currency swap contracts [Member]	Sep. 30, 2012 Forward interest rate contracts [Member]	Jun. 30, 2012 Rate adjustment to LIBOR on Interest Rate Swap Agreements [Member]
Derivative Instruments Gain Loss [Line Items]
Notional amount										$ 3,000,000,000	$ 3,500,000,000	$ 261,000,000	$ 292,000,000
Amounts expected to be reclassified from Accumulated Other Comprehensive Income into earnings over the next 12 months - gains (losses)														3,000,000
Amounts expected to be reclassified from Accumulated Other Comprehensive Income into earnings over the next 12 months - gain (loss)															(1,000,000)
Derivative lower range variable interest rate																0.30%
Derivative higher range variable interest rate																2.60%
Receipt from counterparties upon termination of interest rate swap contracts						397,000,000
Unrealized gain (loss) on the hedged debt							(149,000,000)	(20,000,000)	(186,000,000)
Unrealized gain (loss) on interest rate swaps							149,000,000	20,000,000	186,000,000
Foreign currency open contracts - not designated as hedges - notional amounts										743,000,000	389,000,000
Derivative instruments (Textual) [Abstract]
Length of time hedged in foreign currency contracts			primarily over a three-year time horizon
Ineffective portions of cash flow hedging instruments (approximately), Gain (loss)	(1,000,000)	1,000,000	(1,000,000)	1,000,000
Interest rate swap contracts - fair value hedge - notional amounts					$ 3,600,000,000