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Derivative instruments (Details Textual) (USD $)
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3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | ||||||||||||
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Sep. 30, 2012
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Sep. 30, 2011
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Sep. 30, 2012
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Sep. 30, 2011
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Dec. 31, 2011
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Jun. 30, 2012
Net cash provided by operating activities [Member]
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Sep. 30, 2011
Interest expense, net [Member]
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Sep. 30, 2012
Interest expense, net [Member]
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Sep. 30, 2011
Interest expense, net [Member]
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Sep. 30, 2012
Foreign currency forward contracts [Member]
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Dec. 31, 2011
Foreign currency forward contracts [Member]
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Sep. 30, 2012
Foreign currency option contracts [Member]
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Dec. 31, 2011
Foreign currency option contracts [Member]
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Sep. 30, 2012
Foreign currency and cross currency swap contracts [Member]
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Sep. 30, 2012
Forward interest rate contracts [Member]
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Jun. 30, 2012
Rate adjustment to LIBOR on Interest Rate Swap Agreements [Member]
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| 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 | |||||||||||||||