Supplemental Oil and Gas Information (Results of Operations for Oil andGas Producing Activities) (Details) - USD ($)		3 Months Ended	12 Months Ended
		Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues
Revenues	[1]		$ 1,799,500,000	$ 2,775,000,000	$ 5,273,100,000
Other operating revenues	[1]		5,100,000	159,700,000	149,600,000
Total revenues	[1]		1,804,600,000	2,934,700,000	5,422,700,000
Costs and expenses
Lease operating expenses	[1]		559,400,000	832,300,000	1,089,900,000
Severance and ad valorem taxes	[1]		43,800,000	65,800,000	107,200,000
Exploration costs charged to expense	[1]		58,500,000	395,500,000	439,200,000
Undeveloped lease amortization	[1]		43,400,000	75,400,000	74,400,000
Depreciation, depletion and amortization	[1]		1,037,300,000	1,607,900,000	1,897,500,000
Accretion of asset retirement obligations	[1]		46,700,000	48,700,000	50,800,000
Impairment of assets			95,088,000	2,493,156,000	51,314,000
Redetermination expense	[1]		39,100,000
Deepwater rig contract exit costs			(4,344,000)	282,001,000
Selling and general expenses	[1]		147,400,000	177,200,000	212,000,000
Other expenses	[1]		18,200,000	78,600,000	24,900,000
Total costs and expenses	[1]		2,084,600,000	6,056,600,000	3,947,200,000
Results of operations before taxes	[1]		(280,000,000)	(3,121,900,000)	1,475,500,000
Income tax expense (benefit)	[1]		(155,100,000)	(1,111,000,000)	285,700,000
Results of operations	[1]		(124,900,000)	(2,010,900,000)	1,189,800,000
Crude Oil and Natural Gas Liquids [Member]
Revenues
Revenues	[1]		1,506,800,000	2,351,500,000	4,587,100,000
Natural Gas [Member]
Revenues
Revenues	[1]		292,700,000	423,500,000	686,000,000
United States [Member]
Revenues
Revenues	[1]		685,800,000	1,247,300,000	2,189,300,000
Other operating revenues	[1]		(100,000)	6,300,000	7,100,000
Total revenues	[1]		685,700,000	1,253,600,000	2,196,400,000
Costs and expenses
Lease operating expenses	[1]		218,600,000	312,000,000	345,500,000
Severance and ad valorem taxes	[1]		37,000,000	55,900,000	96,500,000
Exploration costs charged to expense	[1]		6,100,000	258,200,000	129,800,000
Undeveloped lease amortization	[1]		38,400,000	59,200,000	50,100,000
Depreciation, depletion and amortization	[1]		600,500,000	794,900,000	840,700,000
Accretion of asset retirement obligations	[1]		17,100,000	20,200,000	17,500,000
Impairment of assets	[1]			329,000,000	14,300,000
Deepwater rig contract exit costs	[1]		(4,300,000)	282,000,000
Selling and general expenses	[1]		68,800,000	88,200,000	95,200,000
Other expenses	[1]		(3,200,000)	6,700,000	4,900,000
Total costs and expenses	[1]		979,000,000	2,206,300,000	1,594,500,000
Results of operations before taxes	[1]		(293,300,000)	(952,700,000)	601,900,000
Income tax expense (benefit)	[1]		(87,900,000)	(337,000,000)	214,800,000
Results of operations	[1]		(205,400,000)	(615,700,000)	387,100,000
United States [Member] | Crude Oil and Natural Gas Liquids [Member]
Revenues
Revenues	[1]		650,700,000	1,176,900,000	2,062,100,000
United States [Member] | Natural Gas [Member]
Revenues
Revenues	[1]		35,100,000	70,400,000	127,200,000
Canada [Member]
Costs and expenses
Impairment of assets		$ 37,047,000	95,088,000	683,574,000	37,047,000	[2]
Canada [Member] | Conventional [Member]
Revenues
Revenues	[1]		301,700,000	348,700,000	654,600,000
Other operating revenues	[1]		(700,000)	(2,400,000)	(2,400,000)
Total revenues	[1]		301,000,000	346,300,000	652,200,000
Costs and expenses
Lease operating expenses	[1]		102,600,000	102,400,000	160,300,000
Severance and ad valorem taxes	[1]		4,300,000	4,800,000	5,600,000
Exploration costs charged to expense	[1]		3,600,000	700,000	1,700,000
Undeveloped lease amortization	[1]		4,500,000	14,400,000	19,400,000
Depreciation, depletion and amortization	[1]		186,700,000	211,200,000	262,700,000
Accretion of asset retirement obligations	[1]		10,900,000	7,200,000	6,000,000
Impairment of assets	[1]		95,100,000	683,600,000	37,000,000
Selling and general expenses	[1]		28,600,000	25,500,000	26,700,000
Other expenses	[1]		7,500,000	43,900,000	1,000,000
Total costs and expenses	[1]		443,800,000	1,093,700,000	520,400,000
Results of operations before taxes	[1]		(142,800,000)	(747,400,000)	131,800,000
Income tax expense (benefit)	[1]		(58,900,000)	(191,200,000)	42,400,000
Results of operations	[1]		(83,900,000)	(556,200,000)	89,400,000
Canada [Member] | Synthetic Oil [Member]
Revenues
Revenues	[1]		60,700,000	203,000,000	391,500,000
Other operating revenues	[1]		3,600,000	400,000	400,000
Total revenues	[1]		64,300,000	203,400,000	391,900,000
Costs and expenses
Lease operating expenses	[1]		69,800,000	166,000,000	233,800,000
Severance and ad valorem taxes	[1]		2,500,000	5,100,000	5,100,000
Depreciation, depletion and amortization	[1]		16,500,000	50,700,000	54,000,000
Accretion of asset retirement obligations	[1]		2,400,000	5,400,000	9,200,000
Selling and general expenses	[1]		500,000	1,000,000	900,000
Total costs and expenses	[1]		91,700,000	228,200,000	303,000,000
Results of operations before taxes	[1]		(27,400,000)	(24,800,000)	88,900,000
Income tax expense (benefit)	[1]		(75,400,000)	2,400,000	21,800,000
Results of operations	[1]		48,000,000	(27,200,000)	67,100,000
Canada [Member] | Crude Oil and Natural Gas Liquids [Member] | Conventional [Member]
Revenues
Revenues	[1]		171,700,000	181,000,000	453,300,000
Canada [Member] | Crude Oil and Natural Gas Liquids [Member] | Synthetic Oil [Member]
Revenues
Revenues	[1]		60,700,000	203,000,000	391,500,000
Canada [Member] | Natural Gas [Member] | Conventional [Member]
Revenues
Revenues	[1]		130,000,000	167,700,000	201,300,000
Malaysia [Member]
Revenues
Revenues	[1]		751,300,000	976,000,000	2,037,700,000
Other operating revenues	[1]		2,100,000	155,400,000	145,800,000
Total revenues	[1]		753,400,000	1,131,400,000	2,183,500,000
Costs and expenses
Lease operating expenses	[1]		168,400,000	251,900,000	350,300,000
Exploration costs charged to expense	[1]		5,200,000	37,600,000	48,700,000
Depreciation, depletion and amortization	[1]		227,700,000	544,900,000	735,000,000
Accretion of asset retirement obligations	[1]		16,300,000	15,900,000	18,100,000
Impairment of assets	[1]			1,480,600,000
Redetermination expense	[1]		39,100,000
Selling and general expenses	[1]		15,900,000	5,700,000	15,700,000
Other expenses	[1]		23,800,000	15,900,000	16,900,000
Total costs and expenses	[1]		496,400,000	2,352,500,000	1,184,700,000
Results of operations before taxes	[1]		257,000,000	(1,221,100,000)	998,800,000
Income tax expense (benefit)	[1]		85,900,000	(567,900,000)	102,600,000
Results of operations	[1]		171,100,000	(653,200,000)	896,200,000
Malaysia [Member] | Crude Oil and Natural Gas Liquids [Member]
Revenues
Revenues	[1]		623,700,000	790,600,000	1,680,200,000
Malaysia [Member] | Natural Gas [Member]
Revenues
Revenues	[1]		127,600,000	185,400,000	357,500,000
Other Regions [Member]
Revenues
Other operating revenues	[1]		200,000		(1,300,000)
Total revenues	[1]		200,000		(1,300,000)
Costs and expenses
Exploration costs charged to expense	[1]		43,600,000	99,000,000	259,000,000
Undeveloped lease amortization	[1]		500,000	1,800,000	4,900,000
Depreciation, depletion and amortization	[1]		5,900,000	6,200,000	5,100,000
Selling and general expenses	[1]		33,600,000	56,800,000	73,500,000
Other expenses	[1]		(9,900,000)	12,100,000	2,100,000
Total costs and expenses	[1]		73,700,000	175,900,000	344,600,000
Results of operations before taxes	[1]		(73,500,000)	(175,900,000)	(345,900,000)
Income tax expense (benefit)	[1]		(18,800,000)	(17,300,000)	(95,900,000)
Results of operations	[1]		$ (54,700,000)	$ (158,600,000)	$ (250,000,000)

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

[2] This amount represented the writeoff of goodwill associated with an oil and gas company acquired in 2000.