Segment Information (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013		Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues	$ 1,035,000,000		$ 862,000,000		$ 2,148,000,000		$ 1,595,000,000
Operating income (loss)	367,000,000		325,000,000		802,000,000		577,000,000
Other gain, net			1,000,000		1,000,000
Gain (loss) on derivatives	(8,000,000)		93,000,000		(108,000,000)		64,000,000
Depreciation, depletion and amortization	230,000,000		187,000,000		455,000,000		366,000,000
Interest expense	12,000,000	[1]	9,000,000	[1]	25,000,000	[1]	19,000,000	[1]
Provision for income taxes	140,000,000	[1]	164,000,000	[1]	269,000,000	[1]	249,000,000	[1]
Assets	8,887,000,000		7,635,000,000		8,887,000,000		7,635,000,000		8,048,000,000
Capital investments	721,000,000	[2]	695,000,000	[2]	1,263,000,000	[2]	1,213,000,000	[2]
Change in accrued expenditures	56,000,000		8,000,000		61,000,000		40,000,000
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	821,000,000		643,000,000		1,740,000,000		1,142,000,000
Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenues	721,000,000		617,000,000		1,517,000,000		1,126,000,000
Operating income (loss)	275,000,000		253,000,000		627,000,000		428,000,000
Other gain, net			1,000,000		1,000,000
Gain (loss) on derivatives	(7,000,000)		93,000,000		(107,000,000)		64,000,000
Depreciation, depletion and amortization	216,000,000		174,000,000		427,000,000		342,000,000
Interest expense	10,000,000	[1]	6,000,000	[1]	18,000,000	[1]	14,000,000	[1]
Provision for income taxes	105,000,000	[1]	138,000,000	[1]	202,000,000	[1]	194,000,000	[1]
Assets	7,127,000,000		6,006,000,000		7,127,000,000		6,006,000,000
Capital investments	676,000,000	[2]	631,000,000	[2]	1,175,000,000	[2]	1,107,000,000	[2]
Exploration and Production [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	4,000,000		2,000,000		10,000,000		3,000,000
Exploration and Production [Member] | Canada [Member]
Segment Reporting Information [Line Items]
Assets	85,000,000		51,000,000		85,000,000		51,000,000
Midstream Services [Member]
Segment Reporting Information [Line Items]
Revenues	314,000,000		245,000,000		631,000,000		469,000,000
Operating income (loss)	93,000,000		73,000,000		175,000,000		149,000,000
Gain (loss) on derivatives	(1,000,000)				(1,000,000)
Depreciation, depletion and amortization	14,000,000		13,000,000		28,000,000		24,000,000
Interest expense	2,000,000	[1]	3,000,000	[1]	7,000,000	[1]	5,000,000	[1]
Provision for income taxes	35,000,000	[1]	26,000,000	[1]	67,000,000	[1]	55,000,000	[1]
Assets	1,532,000,000		1,384,000,000		1,532,000,000		1,384,000,000
Capital investments	36,000,000	[2]	57,000,000	[2]	75,000,000	[2]	95,000,000	[2]
Midstream Services [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	817,000,000		642,000,000		1,730,000,000		1,139,000,000
Other [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	(1,000,000)		(1,000,000)
Assets	228,000,000	[3]	245,000,000	[3]	228,000,000	[3]	245,000,000	[3]
Capital investments	9,000,000	[2]	7,000,000	[2]	13,000,000	[2]	11,000,000	[2]
Other [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues			(1,000,000)
Marketing [Member] | Midstream Services [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	$ 725,000,000		$ 559,000,000		$ 1,549,000,000		$ 979,000,000

[1] Interest expense and the provision for income taxes by segment are allocated as they are incurred at the corporate level.

[2] Capital investments includes increases of $56 million and $8 million for the three month periods ended June 30, 2014 and 2013, respectively, and increases of $61 million and $40 million for the six month periods ended June 30, 2014 and 2013, respectively, relating to the change in accrued expenditures between periods.

[3] Other assets represent corporate assets not allocated to segments and assets for non reportable segments.