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, 2015	Dec. 31, 2014		Dec. 31, 2013
Revenues
Revenues			$ 2,775,000,000	$ 5,273,100,000		$ 5,306,300,000	[1]
Other operating revenues			159,700,000	149,600,000		6,300,000	[1]
Total revenues			2,934,700,000	5,422,700,000		5,312,600,000	[1]
Costs and expenses
Lease operating expenses			832,300,000	1,089,900,000		1,252,900,000	[1]
Severance and ad valorem taxes			65,800,000	107,200,000		87,300,000	[1]
Exploration costs charged to expense			395,500,000	439,200,000		435,300,000	[1]
Undeveloped lease amortization			75,400,000	74,400,000		66,900,000	[1]
Depreciation, depletion and amortization			1,607,900,000	1,897,500,000		1,543,600,000	[1]
Accretion of asset retirement obligations			48,700,000	50,800,000		49,000,000	[1]
Impairment of assets			2,493,156,000	51,314,000		21,587,000
Deepwater rig contract exit costs			282,001,000
Selling and general expenses			177,200,000	212,000,000		170,900,000	[1]
Other expenses			78,600,000	24,900,000
Total costs and expenses			6,056,600,000	3,947,200,000		3,627,500,000	[1]
Results of operations before taxes			(3,121,900,000)	1,475,500,000		1,685,100,000	[1]
Income tax expense (benefit)			(1,111,000,000)	285,700,000		656,300,000	[1]
Results of operations			(2,010,900,000)	1,189,800,000		1,028,800,000	[1]
Crude Oil and Natural Gas Liquids [Member]
Revenues
Revenues			2,351,500,000	4,587,100,000		4,631,500,000	[1]
Natural Gas [Member]
Revenues
Revenues			423,500,000	686,000,000		674,800,000	[1]
United States [Member]
Revenues
Revenues			1,247,300,000	2,189,300,000
Other operating revenues			6,300,000	7,100,000
Total revenues			1,253,600,000	2,196,400,000
Costs and expenses
Lease operating expenses			312,000,000	345,500,000
Severance and ad valorem taxes			55,900,000	96,500,000
Exploration costs charged to expense			258,200,000	129,800,000
Undeveloped lease amortization			59,200,000	50,100,000
Depreciation, depletion and amortization			794,900,000	840,700,000
Accretion of asset retirement obligations			20,200,000	17,500,000
Impairment of assets			328,982,000	14,267,000
Deepwater rig contract exit costs			282,000,000
Selling and general expenses			88,200,000	95,200,000
Other expenses			6,700,000	4,900,000
Total costs and expenses			2,206,300,000	1,594,500,000
Results of operations before taxes			(952,700,000)	601,900,000
Income tax expense (benefit)			(337,000,000)	214,800,000
Results of operations			(615,700,000)	387,100,000
United States [Member] | Oil Reserves [Member]
Revenues
Revenues	[1]					1,797,400,000
Other operating revenues	[1]					6,400,000
Total revenues	[1]					1,803,800,000
Costs and expenses
Lease operating expenses	[1]					273,600,000
Severance and ad valorem taxes	[1]					77,500,000
Exploration costs charged to expense	[1]					75,200,000
Undeveloped lease amortization	[1]					30,300,000
Depreciation, depletion and amortization	[1]					576,300,000
Accretion of asset retirement obligations	[1]					13,500,000
Selling and general expenses	[1]					80,400,000
Total costs and expenses	[1]					1,126,800,000
Results of operations before taxes	[1]					677,000,000
Income tax expense (benefit)	[1]					241,600,000
Results of operations	[1]					435,400,000
United States [Member] | Crude Oil and Natural Gas Liquids [Member]
Revenues
Revenues			1,176,900,000	2,062,100,000
United States [Member] | Crude Oil and Natural Gas Liquids [Member] | Oil Reserves [Member]
Revenues
Revenues	[1]					1,724,700,000
United States [Member] | Natural Gas [Member]
Revenues
Revenues			70,400,000	127,200,000
United States [Member] | Natural Gas [Member] | Oil Reserves [Member]
Revenues
Revenues	[1]					72,700,000
Canada [Member]
Costs and expenses
Impairment of assets		$ 37,047,000
Canada [Member] | Conventional [Member]
Revenues
Revenues			348,700,000	654,600,000		705,300,000	[1]
Other operating revenues			(2,400,000)	(2,400,000)		(1,900,000)	[1]
Total revenues			346,300,000	652,200,000		703,400,000	[1]
Costs and expenses
Lease operating expenses			102,400,000	160,300,000		180,500,000	[1]
Severance and ad valorem taxes			4,800,000	5,600,000		5,000,000	[1]
Exploration costs charged to expense			700,000	1,700,000		32,800,000	[1]
Undeveloped lease amortization			14,400,000	19,400,000		21,000,000	[1]
Depreciation, depletion and amortization			211,200,000	262,700,000		319,200,000	[1]
Accretion of asset retirement obligations			7,200,000	6,000,000		5,900,000	[1]
Impairment of assets			683,574,000	37,047,000	[2]	21,587,000
Selling and general expenses			25,500,000	26,700,000		25,300,000	[1]
Other expenses			43,900,000	1,000,000
Total costs and expenses			1,093,700,000	520,400,000		611,300,000	[1]
Results of operations before taxes			(747,400,000)	131,800,000		92,100,000	[1]
Income tax expense (benefit)			(191,200,000)	42,400,000		19,900,000	[1]
Results of operations			(556,200,000)	89,400,000		72,200,000	[1]
Canada [Member] | Synthetic Oil [Member]
Revenues
Revenues			203,000,000	391,500,000		441,000,000	[1]
Other operating revenues			400,000	400,000		300,000	[1]
Total revenues			203,400,000	391,900,000		441,300,000	[1]
Costs and expenses
Lease operating expenses			166,000,000	233,800,000		223,400,000	[1]
Severance and ad valorem taxes			5,100,000	5,100,000		4,800,000	[1]
Depreciation, depletion and amortization			50,700,000	54,000,000		55,400,000	[1]
Accretion of asset retirement obligations			5,400,000	9,200,000		10,300,000	[1]
Selling and general expenses			1,000,000	900,000		900,000	[1]
Total costs and expenses			228,200,000	303,000,000		294,800,000	[1]
Results of operations before taxes			(24,800,000)	88,900,000		146,500,000	[1]
Income tax expense (benefit)			2,400,000	21,800,000		37,900,000	[1]
Results of operations			(27,200,000)	67,100,000		108,600,000	[1]
Canada [Member] | Crude Oil and Natural Gas Liquids [Member] | Conventional [Member]
Revenues
Revenues			181,000,000	453,300,000		507,200,000	[1]
Canada [Member] | Crude Oil and Natural Gas Liquids [Member] | Synthetic Oil [Member]
Revenues
Revenues			203,000,000	391,500,000		441,000,000	[1]
Canada [Member] | Natural Gas [Member] | Conventional [Member]
Revenues
Revenues			167,700,000	201,300,000		198,100,000	[1]
Malaysia [Member]
Revenues
Revenues			976,000,000	2,037,700,000
Other operating revenues			155,400,000	145,800,000
Total revenues			1,131,400,000	2,183,500,000
Costs and expenses
Lease operating expenses			251,900,000	350,300,000
Exploration costs charged to expense			37,600,000	48,700,000
Depreciation, depletion and amortization			544,900,000	735,000,000
Accretion of asset retirement obligations			15,900,000	18,100,000
Impairment of assets			1,480,600,000
Selling and general expenses			5,700,000	15,700,000
Other expenses			15,900,000	16,900,000
Total costs and expenses			2,352,500,000	1,184,700,000
Results of operations before taxes			(1,221,100,000)	998,800,000
Income tax expense (benefit)			(567,900,000)	102,600,000
Results of operations			(653,200,000)	896,200,000
Malaysia [Member] | Oil Reserves [Member]
Revenues
Revenues	[1]					2,279,000,000
Other operating revenues	[1]					1,500,000
Total revenues	[1]					2,280,500,000
Costs and expenses
Lease operating expenses	[1]					384,400,000
Exploration costs charged to expense	[1]					25,300,000
Depreciation, depletion and amortization	[1]					588,200,000
Accretion of asset retirement obligations	[1]					15,000,000
Selling and general expenses	[1]					3,500,000
Total costs and expenses	[1]					1,016,400,000
Results of operations before taxes	[1]					1,264,100,000
Income tax expense (benefit)	[1]					477,700,000
Results of operations	[1]					786,400,000
Malaysia [Member] | Crude Oil and Natural Gas Liquids [Member]
Revenues
Revenues			790,600,000	1,680,200,000
Malaysia [Member] | Crude Oil and Natural Gas Liquids [Member] | Oil Reserves [Member]
Revenues
Revenues	[1]					1,875,000,000
Malaysia [Member] | Natural Gas [Member]
Revenues
Revenues			185,400,000	357,500,000
Malaysia [Member] | Natural Gas [Member] | Oil Reserves [Member]
Revenues
Revenues	[1]					404,000,000
Other Regions [Member]
Revenues
Other operating revenues				(1,300,000)
Total revenues				(1,300,000)
Costs and expenses
Exploration costs charged to expense			99,000,000	259,000,000
Undeveloped lease amortization			1,800,000	4,900,000
Depreciation, depletion and amortization			6,200,000	5,100,000
Selling and general expenses			56,800,000	73,500,000
Other expenses			12,100,000	2,100,000
Total costs and expenses			175,900,000	344,600,000
Results of operations before taxes			(175,900,000)	(345,900,000)
Income tax expense (benefit)			(17,300,000)	(95,900,000)
Results of operations			$ (158,600,000)	$ (250,000,000)
Other Regions [Member] | Oil Reserves [Member]
Revenues
Revenues	[1]					83,600,000
Total revenues	[1]					83,600,000
Costs and expenses
Lease operating expenses	[1]					191,000,000
Exploration costs charged to expense	[1]					302,000,000
Undeveloped lease amortization	[1]					15,600,000
Depreciation, depletion and amortization	[1]					4,500,000
Accretion of asset retirement obligations	[1]					4,300,000
Selling and general expenses	[1]					60,800,000
Total costs and expenses	[1]					578,200,000
Results of operations before taxes	[1]					(494,600,000)
Income tax expense (benefit)	[1]					(120,800,000)
Results of operations	[1]					(373,800,000)
Other Regions [Member] | Crude Oil and Natural Gas Liquids [Member] | Oil Reserves [Member]
Revenues
Revenues	[1]					$ 83,600,000

[1] CanadaUnitedConven-(Millions of dollars)StatestionalSyntheticMalaysiaOtherTotalYear Ended December 31, 2013Revenues Crude oil and natural gas liquids sales$ 1,724.7 507.2 441.0 1,875.0 83.6 4,631.5 Natural gas sales 72.7 198.1 - 404.0 - 674.8 Total oil and gas revenues 1,797.4 705.3 441.0 2,279.0 83.6 5,306.3 Other operating revenues 6.4 (1.9) 0.3 1.5 - 6.3 Total revenues 1,803.8 703.4 441.3 2,280.5 83.6 5,312.6Costs and expenses Lease operating expenses 273.6 180.5 223.4 384.4 191.0 1,252.9 Severance and ad valorem taxes 77.5 5.0 4.8 - - 87.3 Exploration costs charged to expense 75.2 32.8 - 25.3 302.0 435.3 Undeveloped lease amortization 30.3 21.0 - - 15.6 66.9 Depreciation, depletion and amortization 576.3 319.2 55.4 588.2 4.5 1,543.6 Accretion of asset retirement obligations 13.5 5.9 10.3 15.0 4.3 49.0 Impairment of assets - 21.6 - - - 21.6 Selling and general expenses 80.4 25.3 0.9 3.5 60.8 170.9 Total costs and expenses 1,126.8 611.3 294.8 1,016.4 578.2 3,627.5 Results of operations before taxes 677.0 92.1 146.5 1,264.1 (494.6) 1,685.1 Income tax expense (benefit) 241.6 19.9 37.9 477.7 (120.8) 656.3 Results of operations$ 435.4 72.2 108.6 786.4 (373.8) 1,028.8 *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.