Derivative Commodity Instruments (Details) - Derivative Instruments by Income Statement Location (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Gain recognized in OCI on derivative (effective portion), net of tax	$ 49,449,000	$ 42,917,000	$ (47,425,000)	$ 98,385,000
Gain (loss) recognized in OCI on derivative (effective portion), Tax	30,300,000	26,300,000	(29,100,000)	60,300,000
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred	22,600,000
Operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) reclassified from accumulated OCI into income (effective portion)	(5,770,000)	56,666,000	1,821,000	93,390,000
Gain (loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)	(740,000)	175,000	(2,391,000)	1,879,000
Loss recongnized in income on derivative	$ (1,000)	$ (1,000)	$ (1,000)	$ (4,000)