Investments - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended					1 Months Ended	9 Months Ended	1 Months Ended		3 Months Ended	9 Months Ended		3 Months Ended		0 Months Ended	1 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Chesapeake Midstream Partners, L.P.	Sep. 30, 2012 Frac Tech Holdings, L.L.C.	Sep. 30, 2012 Chaparral Energy, Inc.	Jul. 31, 2011 Sundrop Fuels, Inc. gal	Sep. 30, 2012 Sundrop Fuels, Inc.	Dec. 31, 2011 Clean Energy Fuels Corp.	Jul. 31, 2011 Clean Energy Fuels Corp.	Sep. 30, 2012 Clean Energy Fuels Corp.	Sep. 30, 2012 Clean Energy Fuels Corp.	Jul. 11, 2011 Clean Energy Fuels Corp.	Sep. 30, 2012 Twin Eagle Resource Management Llc	Dec. 31, 2010 Twin Eagle Resource Management Llc	Dec. 31, 2011 Gastar Exploration Ltd.	Mar. 31, 2009 Gastar Exploration Ltd.	Sep. 30, 2012 Gastar Exploration Ltd.	Sep. 30, 2012 Utica East Ohio Midstream L.L.C	Mar. 31, 2012 Utica East Ohio Midstream L.L.C	Sep. 30, 2012 Ranch Westex	Dec. 31, 2011 Ranch Westex	Sep. 30, 2012 Glass Mountain Pipeline Limited Liability Company	Apr. 30, 2012 Glass Mountain Pipeline Limited Liability Company mi
Schedule of Equity Method Investments [Line Items]
Cash proceeds from sale of equity method investment	$ 2,000	$ 0	$ 2,000
Gain on sale of equity method investment			1,032
Deferred gain realized related to previously sold equipment to ACMP			13
Positive equity method adjustments			46	71	5		2						6
Cash distribution from the equity investment			56
Equity method accretion adjustments			4	34
Equity Investment Additional Payment				3
Excess carrying value of investment over underlying equity in net assets				633	52		53
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity Attributable to Goodwill				296
Goodwill, Not Allocated, Amount				200
Other Commitment, Due in Next Twelve Months	105
Depreciation					2
Equity method depreciation adjustments					2
Investment in preferred stock						155	115
Expected production of gallons of gasoline from natural gas and waste cellulosic						40,000,000
Equity Method Investment, Permiums Paid							80
Equity method percentage approximate owned			0.00%		20.00%	50.00%				0.00%	0.00%							59.00%	59.00%			50.00%
Investment in newly issued convertible notes									150	50	50	50
Annual interest rate on notes									7.50%
Conversion premium of convertible option into shares									22.50%
Conversion price for convertible promissory note									$ 15.80
Shares purchased								1,000,000
Cost of investment								10									89
Maximum common stock price per share								$ 12.46							$ 3.18
Minimum common stock price per share											$ 13.17						$ 1.66
Equity Method Investment, Other than Temporary Impairment																70
Income (Loss) from Equity Method Investments	(147)	19								3							8
Equity method investment													16	20
Investment total commitment																			474		36
Current Funding Amount Of Investment																				33
Total commitment, funded amount																		75
Additional assets sold, miles of pipeline																							210
Sale of Investment																							47
Gain on Sale of Pipeline																							31
Sale of Remaining Percentage In Investment																							52
Gain on Sale of Investment																							$ 31