Derivative Financial Instruments (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 cubicFeet	Dec. 31, 2010	Dec. 31, 2009
Derivative Financial Instruments [Abstract]
Fair value of collateral provided by the Company	$ 4,000,000	$ 2,000,000
Fair value of cash collateral received from counterparties		1,000,000
Aggregate fair value of HighMount's derivative instruments that are in a net liability position and subject to termination by the counterparties if certain covenants are not complied with	32,000,000
Derivative transactions entered into without hedge designation and not held in a trading portfolio	359,000,000	1,200,000,000
Derivative transactions terminated without hedge designation and not held in a trading portfolio	262,000,000	1,200,000,000
Cubic feet of natural gas equivalents	47,400,000,000
Percentage of commodity hedges with settlement dates in 2012	73.00%
Percentage of commodity hedges with settlement dates in 2013	27.00%
Estimated amount of net unrealized gains associated with commodity contracts that will be reclassified from AOCI into earnings during the next twelve months	29,000,000
Estimated amount of net unrealized gains (losses) associated with foreign exchange contracts that will be reclassified from AOCI into earnings during the next twelve months	(7,000,000)
Estimated amount of net unrealized gains (losses) associated with interest rate swap contracts that will be reclassified from AOCI into earnings during next twelve months	(4,000,000)
Maximum amounts realized due to ineffectiveness	1,000,000	1,000,000	1,000,000
HighMount refinancing variable rate term loan amount	1,100,000,000
Loss on interest rate swaps reclassified from AOCI to earnings	$ (34,000,000)	$ (36,000,000)