Supplemental Oil and Gas Information (Summary of Proved Reserves Based on Average Prices) (Details) MMBbls in Millions, ft³ in Billions	12 Months Ended
	Dec. 31, 2016 MMBbls ft³	Dec. 31, 2015 MMBbls ft³	Dec. 31, 2014 MMBbls ft³	Dec. 31, 2013 MMBbls ft³
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	456.2	441.8	471.2
Revisions of previous estimates	(5.8)	5.3	(9.3)
Improved recovery		2.4	7.5
Extensions and discoveries	11.0	63.8	42.6
Purchases of properties	26.3		6.1
Sales of properties	(121.0)	(11.0)	(24.3)
Production	(37.7)	(46.1)	(52.0)
Proved developed and undeveloped reserves, Ending Balance	329.0	456.2	441.8
Proved developed reserves	184.9	326.6	324.1	289.9
Proved undeveloped reserves	144.1	129.6	117.7	181.3
Crude Oil [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	341.4	336.2	354.2
Revisions of previous estimates	(5.8)	(8.2)	(2.3)
Improved recovery		2.4	7.5
Extensions and discoveries	11.0	63.8	42.6
Purchases of properties	26.3		6.1
Sales of properties	(7.8)	(11.0)	(24.3)
Production	(36.1)	(41.8)	(47.6)
Proved developed and undeveloped reserves, Ending Balance	329.0	341.4	336.2
Proved developed reserves	184.9	211.8	218.5	172.9
Proved undeveloped reserves	144.1	129.6	117.7	181.3
Natural Gas Liquids Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	36.4	30.6	24.4
Revisions of previous estimates	1.6	2.0	5.1
Extensions and discoveries	2.9	7.6	4.7
Purchases of properties	5.1
Sales of properties		(0.1)	(0.2)
Production	(3.5)	(3.7)	(3.4)
Proved developed and undeveloped reserves, Ending Balance	42.5	36.4	30.6
Proved developed reserves	22.2	21.6	17.5	14.2
Proved undeveloped reserves	20.3	14.8	13.1	10.2
Natural Gas Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance | ft³	1,688.8	1,704.7	1,153.6
Revisions of previous estimates | ft³	43.3	53.5	167.2
Improved recovery | ft³		1.8	7.0
Extensions and discoveries | ft³	164.2	162.9	696.8
Purchases of properties | ft³	122.3		5.5
Sales of properties | ft³	(2.2)	(78.0)	(162.6)
Production | ft³	(138.4)	(156.1)	(162.8)
Proved developed and undeveloped reserves, Ending Balance | ft³	1,878.0	1,688.8	1,704.7
Proved developed reserves | ft³	818.1	783.5	812.1	786.2
Proved undeveloped reserves | ft³	1,059.9	905.3	892.6	367.4
United States [Member] | Crude Oil [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	238.9	204.9	191.5
Revisions of previous estimates	(10.9)	(7.6)	(3.2)
Extensions and discoveries	8.6	63.8	32.7
Purchases of properties			6.1
Sales of properties	(4.5)		(0.3)
Production	(17.7)	(22.2)	(21.9)
Proved developed and undeveloped reserves, Ending Balance	214.4	238.9	204.9
Proved developed reserves	113.9	125.9	106.2	75.8
Proved undeveloped reserves	100.5	113.0	98.7	115.7
United States [Member] | Natural Gas Liquids Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	35.4	29.1	23.2
Revisions of previous estimates	1.2	2.2	5.0
Extensions and discoveries	2.8	7.6	4.0
Production	(3.0)	(3.5)	(3.1)
Proved developed and undeveloped reserves, Ending Balance	36.4	35.4	29.1
Proved developed reserves	20.8	20.7	16.5	13.1
Proved undeveloped reserves	15.6	14.7	12.6	10.1
United States [Member] | Natural Gas Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance | ft³	232.4	226.3	185.0
Revisions of previous estimates | ft³	0.1	(5.2)	47.7
Extensions and discoveries | ft³	6.4	43.2	24.1
Purchases of properties | ft³			5.5
Sales of properties | ft³	(0.1)		(3.7)
Production | ft³	(19.4)	(31.9)	(32.3)
Proved developed and undeveloped reserves, Ending Balance | ft³	219.4	232.4	226.3
Proved developed reserves | ft³	138.7	148.3	145.6	112.6
Proved undeveloped reserves | ft³	80.7	84.1	80.7	72.4
Canada [Member] | Crude Oil [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	27.9	37.4	38.7
Revisions of previous estimates	2.5	(4.8)	2.7
Extensions and discoveries			2.4
Purchases of properties	26.3
Sales of properties	(3.3)		(0.5)
Production	(4.5)	(4.7)	(5.9)
Proved developed and undeveloped reserves, Ending Balance	48.9	27.9	37.4
Proved developed reserves	19.2	23.8	32.4	31.6
Proved undeveloped reserves	29.7	4.1	5.0	7.1
Canada [Member] | Synthetic Oil [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	114.8	105.6	117.0
Revisions of previous estimates		13.5	(7.0)
Sales of properties	(113.2)
Production	(1.6)	(4.3)	(4.4)
Proved developed and undeveloped reserves, Ending Balance		114.8	105.6
Proved developed reserves		114.8	105.6	117.0
Canada [Member] | Natural Gas Liquids Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	0.4	0.7	0.1
Revisions of previous estimates	0.2	(0.3)
Extensions and discoveries	0.1		0.6
Purchases of properties	5.1
Production	(0.2)
Proved developed and undeveloped reserves, Ending Balance	5.6	0.4	0.7
Proved developed reserves	0.9	0.3	0.2
Proved undeveloped reserves	4.7	0.1	0.5	0.1
Canada [Member] | Natural Gas Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance | ft³	909.6	842.8	562.8
Revisions of previous estimates | ft³	45.3	18.9	105.6
Extensions and discoveries | ft³	120.2	119.7	231.5
Purchases of properties | ft³	122.3
Sales of properties | ft³	(2.1)
Production | ft³	(76.4)	(71.8)	(57.1)
Proved developed and undeveloped reserves, Ending Balance | ft³	1,118.9	909.6	842.8
Proved developed reserves | ft³	498.9	453.5	467.4	384.0
Proved undeveloped reserves | ft³	620.0	456.1	375.4	178.8
Malaysia [Member] | Crude Oil [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	74.6	93.9	124.0
Revisions of previous estimates	2.6	4.2	(1.8)
Improved recovery		2.4	7.5
Extensions and discoveries	2.4		7.5
Sales of properties		(11.0)	(23.5)
Production	(13.9)	(14.9)	(19.8)
Proved developed and undeveloped reserves, Ending Balance	65.7	74.6	93.9
Proved developed reserves	51.8	62.1	79.9	65.5
Proved undeveloped reserves	13.9	12.5	14.0	58.5
Malaysia [Member] | Natural Gas Liquids Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance	0.6	0.8	1.1
Revisions of previous estimates	0.2	0.1	0.1
Extensions and discoveries			0.1
Sales of properties		(0.1)	(0.2)
Production	(0.3)	(0.2)	(0.3)
Proved developed and undeveloped reserves, Ending Balance	0.5	0.6	0.8
Proved developed reserves	0.5	0.6	0.8	1.1
Malaysia [Member] | Natural Gas Reserves [Member]
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, Beginning Balance | ft³	546.8	635.6	405.8
Revisions of previous estimates | ft³	(2.1)	39.8	13.9
Improved recovery | ft³		1.8	7.0
Extensions and discoveries | ft³	37.6		441.2
Sales of properties | ft³		(78.0)	(158.9)
Production | ft³	(42.6)	(52.4)	(73.4)
Proved developed and undeveloped reserves, Ending Balance | ft³	539.7	546.8	635.6
Proved developed reserves | ft³	180.5	181.7	199.1	289.6
Proved undeveloped reserves | ft³	359.2	365.1	436.5	116.2