Summary of Proved Natural Gas Reserves Based on Year-End Prices for 2007 and 2008 and Average Prices for 2009 and 2010 (Detail) (Natural Gas Reserves)	12 Months Ended
	Dec. 31, 2011 cf	Dec. 31, 2010 cf	Dec. 31, 2009 cf
Proved developed and undeveloped natural gas reserves:
Proved developed and undeveloped reserves, Beginning Balance	883,100,000,000	754,600,000,000	585,600,000,000
Revisions of previous estimates	12,600,000,000	15,200,000,000	77,200,000,000
Improved recovery	13,800,000,000	(1,000,000,000)	6,900,000,000
Extensions and discoveries	363,500,000,000	220,500,000,000	153,500,000,000
Purchases of properties		24,000,000,000
Production	(166,900,000,000)	(130,200,000,000)	(68,400,000,000)
Sales of properties			(200,000,000)
Proved developed and undeveloped reserves, Ending Balance	1,106,100,000,000	883,100,000,000	754,600,000,000
Proved developed reserve	711,600,000,000	586,000,000,000	401,600,000,000
Proved undeveloped reserves	394,500,000,000	297,100,000,000	353,000,000,000
United States
Proved developed and undeveloped natural gas reserves:
Proved developed and undeveloped reserves, Beginning Balance	90,800,000,000	89,300,000,000	97,400,000,000
Revisions of previous estimates	(6,300,000,000)	6,600,000,000	9,100,000,000
Improved recovery	0	0	0
Extensions and discoveries	31,100,000,000	14,300,000,000	2,600,000,000
Purchases of properties		0
Production	(17,200,000,000)	(19,400,000,000)	(19,800,000,000)
Sales of properties			0
Proved developed and undeveloped reserves, Ending Balance	98,400,000,000	90,800,000,000	89,300,000,000
Proved developed reserve	58,200,000,000	67,000,000,000	73,200,000,000
Proved undeveloped reserves	40,200,000,000	23,800,000,000	16,100,000,000
Canada
Proved developed and undeveloped natural gas reserves:
Proved developed and undeveloped reserves, Beginning Balance	326,900,000,000	124,700,000,000	62,200,000,000
Revisions of previous estimates	59,400,000,000	15,200,000,000	(600,000,000)
Improved recovery	0	0	0
Extensions and discoveries	321,500,000,000	194,200,000,000	83,300,000,000
Purchases of properties		24,000,000,000
Production	(68,900,000,000)	(31,200,000,000)	(20,000,000,000)
Sales of properties			(200,000,000)
Proved developed and undeveloped reserves, Ending Balance	638,900,000,000	326,900,000,000	124,700,000,000
Proved developed reserve	427,100,000,000	210,100,000,000	89,700,000,000
Proved undeveloped reserves	211,800,000,000	116,800,000,000	35,000,000,000
Malaysia
Proved developed and undeveloped natural gas reserves:
Proved developed and undeveloped reserves, Beginning Balance	434,000,000,000	511,800,000,000	405,200,000,000
Revisions of previous estimates	(32,500,000,000)	(11,200,000,000)	59,400,000,000
Improved recovery	14,800,000,000	(1,000,000,000)	6,900,000,000
Extensions and discoveries	10,900,000,000	12,000,000,000	67,600,000,000
Purchases of properties		0
Production	(79,400,000,000)	(77,600,000,000)	(27,300,000,000)
Sales of properties			0
Proved developed and undeveloped reserves, Ending Balance	347,800,000,000	434,000,000,000	511,800,000,000
Proved developed reserve	210,500,000,000	277,500,000,000	209,900,000,000
Proved undeveloped reserves	137,300,000,000	156,500,000,000	301,900,000,000
United Kingdom
Proved developed and undeveloped natural gas reserves:
Proved developed and undeveloped reserves, Beginning Balance	31,400,000,000	28,800,000,000	20,800,000,000
Revisions of previous estimates	(8,000,000,000)	4,600,000,000	9,300,000,000
Improved recovery	(1,000,000,000)	0	0
Extensions and discoveries	0	0	0
Purchases of properties		0
Production	(1,400,000,000)	(2,000,000,000)	(1,300,000,000)
Sales of properties			0
Proved developed and undeveloped reserves, Ending Balance	21,000,000,000	31,400,000,000	28,800,000,000
Proved developed reserve	15,800,000,000	31,400,000,000	28,800,000,000
Proved undeveloped reserves	5,200,000,000	0	0