Derivative instruments (Details Textual) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Interest expense, net [Member]	Mar. 31, 2012 Interest expense, net [Member]	Mar. 31, 2013 Foreign currency forward contracts [Member]	Dec. 31, 2012 Foreign currency forward contracts [Member]	Mar. 31, 2013 Foreign currency option contracts [Member]	Dec. 31, 2012 Foreign currency option contracts [Member]	Mar. 31, 2013 Foreign currency and cross currency swap contracts [Member]	Mar. 31, 2013 Forward interest rate contracts [Member]	Mar. 31, 2013 Rate adjustment to LIBOR on Interest Rate Swap Agreements [Member]	Mar. 31, 2012 Rate adjustment to LIBOR on Interest Rate Swap Agreements [Member]
Derivative Instruments Gain Loss [Line Items]
Ineffective portions of cash flow hedging instruments (approximately), gain (loss)	$ 1,000,000	$ (1,000,000)
Length of time hedged in foreign currency contracts	P3Y
Notional amount					3,700,000,000	3,700,000,000	139,000,000	200,000,000
Amounts expected to be reclassified from Accumulated Other Comprehensive Income into earnings over the next 12 months - gains (losses)									25,000,000
Amounts expected to be reclassified from Accumulated Other Comprehensive Income into earnings over the next 12 months - gain (loss)										(1,000,000)
Interest rate swap contracts - fair value hedge - notional amounts	2,500,000,000	3,600,000,000
Derivative lower range variable interest rate											1.60%	0.30%
Derivative higher range variable interest rate											2.00%	2.60%
Unrealized gain (loss) on the hedged debt			(22,000,000)	18,000,000
Unrealized gain (loss) on interest rate swaps			22,000,000	(18,000,000)
Foreign currency open contracts - not designated as hedges - notional amounts					$ 655,000,000	$ 629,000,000