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Derivative instruments (Details Textual) (USD $)
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3 Months Ended | |||||||||||
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Mar. 31, 2013
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Mar. 31, 2012
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Mar. 31, 2013
Interest expense, net [Member]
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Mar. 31, 2012
Interest expense, net [Member]
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Mar. 31, 2013
Foreign currency forward contracts [Member]
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Dec. 31, 2012
Foreign currency forward contracts [Member]
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Mar. 31, 2013
Foreign currency option contracts [Member]
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Dec. 31, 2012
Foreign currency option contracts [Member]
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Mar. 31, 2013
Foreign currency and cross currency swap contracts [Member]
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Mar. 31, 2013
Forward interest rate contracts [Member]
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Mar. 31, 2013
Rate adjustment to LIBOR on Interest Rate Swap Agreements [Member]
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Mar. 31, 2012
Rate adjustment to LIBOR on Interest Rate Swap Agreements [Member]
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| 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 | ||||||||||