Results of Operations for Oil and Gas Producing Activities (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Revenues
Total oil and gas revenues	$ 4,599,600,000	[1]	$ 4,205,400,000	[1]	$ 3,538,800,000	[1]
Other operating revenues	8,500,000	[1]	39,900,000	[1]	17,700,000	[1]
Total revenues	4,608,100,000	[1]	4,245,300,000	[1]	3,556,500,000	[1]
Costs and expenses
Production expenses	1,114,800,000	[1]	1,010,300,000	[1]	852,600,000	[1]
Exploration costs charged to expense	251,100,000	[1]	371,200,000	[1]	168,100,000	[1]
Undeveloped lease amortization	129,800,000	[1]	118,200,000	[1]	108,000,000	[1]
Depreciation, depletion and amortization	1,244,400,000	[1]	956,000,000	[1]	982,600,000	[1]
Accretion of asset retirement obligations	38,400,000	[1]	33,800,000	[1]	28,800,000	[1]
Impairment of properties	200,000,000	[1]	368,600,000	[1]
Terra Nova working interest redetermination	0		(5,351,000)	[1],[2]	18,582,000	[1],[2]
Selling and general expenses	119,600,000	[1]	97,600,000	[1]	77,100,000	[1]
Total costs and expenses	3,098,100,000	[1]	2,950,300,000	[1]	2,235,800,000	[1]
Results of Operations, Income before Income Taxes	1,510,000,000	[1]	1,295,000,000	[1]	1,320,700,000	[1]
Income tax expense (benefit)	605,000,000	[1]	680,800,000	[1]	544,300,000	[1]
Results of operations	905,000,000	[1]	614,200,000	[1]	776,400,000	[1]
Crude Oil and Natural Gas Liquids
Revenues
Sales to unaffiliated enterprises	3,854,500,000	[1]	3,250,000,000	[1]	2,893,700,000	[1]
Transfers to consolidated operations			142,800,000	[1]	118,900,000	[1]
Natural Gas
Revenues
Sales to unaffiliated enterprises	745,100,000	[1]	812,600,000	[1]	526,200,000	[1]
United States | Oil Reserves
Revenues
Total oil and gas revenues	1,030,300,000	[1]	719,900,000	[1]	644,600,000	[1]
Other operating revenues	7,700,000	[1]	17,800,000	[1]	15,300,000	[1]
Total revenues	1,038,000,000	[1]	737,700,000	[1]	659,900,000	[1]
Costs and expenses
Production expenses	252,400,000	[1]	164,800,000	[1]	131,700,000	[1]
Exploration costs charged to expense	51,900,000	[1]	36,500,000	[1]	35,700,000	[1]
Undeveloped lease amortization	71,600,000	[1]	62,200,000	[1]	68,500,000	[1]
Depreciation, depletion and amortization	330,200,000	[1]	183,000,000	[1]	281,100,000	[1]
Accretion of asset retirement obligations	11,400,000	[1]	9,900,000	[1]	6,900,000	[1]
Impairment of properties	0	[1]	0	[1]
Terra Nova working interest redetermination			0	[1]	0	[1]
Selling and general expenses	52,700,000	[1]	42,100,000	[1]	33,300,000	[1]
Total costs and expenses	770,200,000	[1]	498,500,000	[1]	557,200,000	[1]
Results of Operations, Income before Income Taxes	267,800,000	[1]	239,200,000	[1]	102,700,000	[1]
Income tax expense (benefit)	99,800,000	[1]	86,500,000	[1]	30,000,000	[1]
Results of operations	168,000,000	[1]	152,700,000	[1]	72,700,000	[1]
United States | Crude Oil and Natural Gas Liquids | Oil Reserves
Revenues
Sales to unaffiliated enterprises	976,100,000	[1]	648,800,000	[1]	557,600,000	[1]
Transfers to consolidated operations			0	[1]	0	[1]
United States | Natural Gas | Oil Reserves
Revenues
Sales to unaffiliated enterprises	54,200,000	[1]	71,100,000	[1]	87,000,000	[1]
Canada | Conventional
Revenues
Total oil and gas revenues	621,500,000	[1]	785,800,000	[1]	520,700,000	[1]
Other operating revenues	(900,000)	[1]	(3,800,000)	[1]	(200,000)	[1]
Total revenues	620,600,000	[1]	782,000,000	[1]	520,500,000	[1]
Costs and expenses
Production expenses	167,200,000	[1]	151,200,000	[1]	97,500,000	[1]
Exploration costs charged to expense	10,500,000	[1]	60,800,000	[1]	1,900,000	[1]
Undeveloped lease amortization	29,300,000	[1]	28,800,000	[1]	33,700,000	[1]
Depreciation, depletion and amortization	290,500,000	[1]	273,900,000	[1]	180,300,000	[1]
Accretion of asset retirement obligations	5,100,000	[1]	4,900,000	[1]	4,800,000	[1]
Impairment of properties	0	[1]	0	[1]
Terra Nova working interest redetermination			(5,400,000)	[1]	18,600,000	[1]
Selling and general expenses	19,700,000	[1]	14,200,000	[1]	10,500,000	[1]
Total costs and expenses	522,300,000	[1]	528,400,000	[1]	347,300,000	[1]
Results of Operations, Income before Income Taxes	98,300,000	[1]	253,600,000	[1]	173,200,000	[1]
Income tax expense (benefit)	25,100,000	[1]	79,700,000	[1]	44,600,000	[1]
Results of operations	73,200,000	[1]	173,900,000	[1]	128,600,000	[1]
Canada | Synthetic Oil
Revenues
Total oil and gas revenues	463,100,000	[1]	506,600,000	[1]	378,600,000	[1]
Other operating revenues	600,000	[1]	0	[1]	0	[1]
Total revenues	463,700,000	[1]	506,600,000	[1]	378,600,000	[1]
Costs and expenses
Production expenses	224,100,000	[1]	236,100,000	[1]	206,400,000	[1]
Exploration costs charged to expense	0	[1]	0	[1]	0	[1]
Undeveloped lease amortization	0	[1]	0	[1]	0	[1]
Depreciation, depletion and amortization	55,300,000	[1]	52,100,000	[1]	45,200,000	[1]
Accretion of asset retirement obligations	8,500,000	[1]	7,600,000	[1]	6,400,000	[1]
Impairment of properties	0	[1]	0	[1]
Terra Nova working interest redetermination			0	[1]	0	[1]
Selling and general expenses	900,000	[1]	900,000	[1]	900,000	[1]
Total costs and expenses	288,800,000	[1]	296,700,000	[1]	258,900,000	[1]
Results of Operations, Income before Income Taxes	174,900,000	[1]	209,900,000	[1]	119,700,000	[1]
Income tax expense (benefit)	40,000,000	[1]	55,800,000	[1]	34,500,000	[1]
Results of operations	134,900,000	[1]	154,100,000	[1]	85,200,000	[1]
Canada | Crude Oil and Natural Gas Liquids | Conventional
Revenues
Sales to unaffiliated enterprises	411,700,000	[1]	459,200,000	[1]	346,400,000	[1]
Transfers to consolidated operations			46,400,000	[1]	42,200,000	[1]
Canada | Crude Oil and Natural Gas Liquids | Synthetic Oil
Revenues
Sales to unaffiliated enterprises	463,100,000	[1]	410,200,000	[1]	301,900,000	[1]
Transfers to consolidated operations			96,400,000	[1]	76,700,000	[1]
Canada | Natural Gas | Conventional
Revenues
Sales to unaffiliated enterprises	209,800,000	[1]	280,200,000	[1]	132,100,000	[1]
Canada | Natural Gas | Synthetic Oil
Revenues
Sales to unaffiliated enterprises	0	[1]	0	[1]	0	[1]
Malaysia | Oil Reserves
Revenues
Total oil and gas revenues	2,427,100,000	[1]	2,044,300,000	[1]	1,838,200,000	[1]
Other operating revenues	1,000,000	[1]	1,300,000	[1]	(300,000)	[1]
Total revenues	2,428,100,000	[1]	2,045,600,000	[1]	1,837,900,000	[1]
Costs and expenses
Production expenses	422,700,000	[1]	420,600,000	[1]	355,000,000	[1]
Exploration costs charged to expense	27,200,000	[1]	11,100,000	[1]	19,800,000	[1]
Undeveloped lease amortization	0	[1]	0	[1]	0	[1]
Depreciation, depletion and amortization	532,100,000	[1]	357,300,000	[1]	379,000,000	[1]
Accretion of asset retirement obligations	12,500,000	[1]	10,600,000	[1]	9,800,000	[1]
Impairment of properties	0	[1]	0	[1]
Terra Nova working interest redetermination			0	[1]	0	[1]
Selling and general expenses	(5,300,000)	[1]	(1,600,000)	[1]	800,000	[1]
Total costs and expenses	989,200,000	[1]	798,000,000	[1]	764,400,000	[1]
Results of Operations, Income before Income Taxes	1,438,900,000	[1]	1,247,600,000	[1]	1,073,500,000	[1]
Income tax expense (benefit)	544,700,000	[1]	434,900,000	[1]	414,100,000	[1]
Results of operations	894,200,000	[1]	812,700,000	[1]	659,400,000	[1]
Malaysia | Crude Oil and Natural Gas Liquids | Oil Reserves
Revenues
Sales to unaffiliated enterprises	1,946,000,000	[1]	1,583,000,000	[1]	1,531,100,000	[1]
Transfers to consolidated operations			0	[1]	0	[1]
Malaysia | Natural Gas | Oil Reserves
Revenues
Sales to unaffiliated enterprises	481,100,000	[1]	461,300,000	[1]	307,100,000	[1]
Republic of the Congo | Oil Reserves
Revenues
Total oil and gas revenues	57,600,000	[1]	148,800,000	[1]	156,700,000	[1]
Other operating revenues	0	[1]	0	[1]	(1,000,000)	[1]
Total revenues	57,600,000	[1]	148,800,000	[1]	155,700,000	[1]
Costs and expenses
Production expenses	48,400,000	[1]	37,600,000	[1]	62,000,000	[1]
Exploration costs charged to expense	76,800,000	[1]	21,000,000	[1]	56,400,000	[1]
Undeveloped lease amortization	0	[1]	0	[1]	0	[1]
Depreciation, depletion and amortization	33,900,000	[1]	87,800,000	[1]	95,500,000	[1]
Accretion of asset retirement obligations	900,000	[1]	500,000	[1]	400,000	[1]
Impairment of properties	200,000,000	[1]	368,600,000	[1]
Terra Nova working interest redetermination			0	[1]	0	[1]
Selling and general expenses	3,200,000	[1]	2,200,000	[1]	(2,000,000)	[1]
Total costs and expenses	363,200,000	[1]	517,700,000	[1]	212,300,000	[1]
Results of Operations, Income before Income Taxes	(305,600,000)	[1]	(368,900,000)	[1]	(56,600,000)	[1]
Income tax expense (benefit)	(64,500,000)	[1]	16,400,000	[1]	20,600,000	[1]
Results of operations	(241,100,000)	[1]	(385,300,000)	[1]	(77,200,000)	[1]
Republic of the Congo | Crude Oil and Natural Gas Liquids | Oil Reserves
Revenues
Sales to unaffiliated enterprises	57,600,000	[1]	148,800,000	[1]	156,700,000	[1]
Transfers to consolidated operations			0	[1]	0	[1]
Republic of the Congo | Natural Gas | Oil Reserves
Revenues
Sales to unaffiliated enterprises	0	[1]	0	[1]	0	[1]
Other Regions | Oil Reserves
Revenues
Total oil and gas revenues	0	[1]	0	[1]	0	[1]
Other operating revenues	100,000	[1]	24,600,000	[1]	3,900,000	[1]
Total revenues	100,000	[1]	24,600,000	[1]	3,900,000	[1]
Costs and expenses
Production expenses	0	[1]	0	[1]	0	[1]
Exploration costs charged to expense	84,700,000	[1]	241,800,000	[1]	54,300,000	[1]
Undeveloped lease amortization	28,900,000	[1]	27,200,000	[1]	5,800,000	[1]
Depreciation, depletion and amortization	2,400,000	[1]	1,900,000	[1]	1,500,000	[1]
Accretion of asset retirement obligations	0	[1]	300,000	[1]	500,000	[1]
Impairment of properties	0	[1]	0	[1]
Terra Nova working interest redetermination			0	[1]	0	[1]
Selling and general expenses	48,400,000	[1]	39,800,000	[1]	33,600,000	[1]
Total costs and expenses	164,400,000	[1]	311,000,000	[1]	95,700,000	[1]
Results of Operations, Income before Income Taxes	(164,300,000)	[1]	(286,400,000)	[1]	(91,800,000)	[1]
Income tax expense (benefit)	(40,100,000)	[1]	7,500,000	[1]	500,000	[1]
Results of operations	(124,200,000)	[1]	(293,900,000)	[1]	(92,300,000)	[1]
Other Regions | Crude Oil and Natural Gas Liquids | Oil Reserves
Revenues
Sales to unaffiliated enterprises	0	[1]	0	[1]	0	[1]
Transfers to consolidated operations			0	[1]	0	[1]
Other Regions | Natural Gas | Oil Reserves
Revenues
Sales to unaffiliated enterprises	$ 0	[1]	$ 0	[1]	$ 0	[1]

[1] Results exclude corporate overhead, interest and discontinued operations.

[2] Reclassified to conform to current presentation.