Derivative Instruments and Hedging Activities (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012 CounterParty
Derivative Instruments and Hedging Activities (Textual) [Abstract]
Number of counterparties	18
Realization of gains and losses on hedges in future earnings	mid 2014
Net gain included in accumulated other comprehensive income (loss), before tax applied to next twelve months	$ 112
Net gain included in accumulated other comprehensive income (loss), after tax	$ 100
2012 [Member]
Derivative [Line Items]
Percentage of collars derivative settled in 2012	29.00%
2013 [Member]
Derivative [Line Items]
Percentage of collars derivative settled in 2013	58.00%

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Net gain included in accumulated other comprehensive income loss after tax.

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Net gain included in accumulated other comprehensive income loss before tax.

No definition available.

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Number of counterparties.

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Percentage of collars derivative settled in two thousand and thirteen

No definition available.

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Percentage of collars derivative settled in two thousand and twelve.

No definition available.

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Realization of gains and losses on hedges in future earnings.

No definition available.

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