Derivative Commodity Instruments (Details) - Derivative Instruments by Income Statement Location (USD $)	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Gain recognized in OCI on derivative (effective portion), net of tax	$ 172,430,000	$ (7,244,000)	$ 125,005,000	$ 91,141,000
Gain (loss) recognized in OCI on derivative (effective portion), Tax	105,700,000	(4,400,000)	76,600,000	55,900,000
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	37,400,000
Operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) reclassified from accumulated OCI into income (effective portion)	11,207,000	56,456,000	13,028,000	149,845,000
Gain (loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)	5,631,000	(1,861,000)	3,240,000	18,000
Gain (loss) recongnized in income on derivative	$ 53,227,000	$ 0	$ 53,225,000	$ (4,000)

Tax effect on the change in OCI gains and losses from derivative instruments designated and qualifying as the effective portion of cash flow hedges.

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The estimated value of gains (losses), net anticipated to be transferred in the future from accumulated other comprehensive income into earnings.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

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The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

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The amount of loss recognized in income during the period on derivative instruments designated and qualifying as hedging instruments in fair value hedges and related hedged items designated and qualifying in fair value hedges, on derivative instruments designated and qualifying as hedging instruments in cash flow hedges, and on derivative instruments not designated as hedging instruments.

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