Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 933us-gaap_Revenues	$ 1,113us-gaap_Revenues
Operating income (loss)	165us-gaap_OperatingIncomeLoss	435us-gaap_OperatingIncomeLoss
Other income (loss), net	(1)us-gaap_OtherNonoperatingIncomeExpense	1us-gaap_OtherNonoperatingIncomeExpense
Gain (loss) on derivatives	14	(100)
Depreciation, depletion and amortization	293us-gaap_DepreciationAndAmortization	225us-gaap_DepreciationAndAmortization
Interest expense	51us-gaap_InterestExpense	13us-gaap_InterestExpense
Provision (benefit) for income taxes	49us-gaap_IncomeTaxExpenseBenefit	129us-gaap_IncomeTaxExpenseBenefit
Assets	15,587us-gaap_Assets	8,423us-gaap_Assets	14,925us-gaap_Assets
Capital investments	1,171	542
Change in accrued expenditures		6
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(661)	(919)
Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenues	660	796
Operating income (loss)	78	352
Other income (loss), net	(1)	2
Gain (loss) on derivatives	15	(100)
Depreciation, depletion and amortization	278	211
Interest expense	45	9
Provision (benefit) for income taxes	18	98
Assets	13,703	6,621
Capital investments	1,030	499
Exploration and Production [Member] \| Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	5	(6)
Exploration and Production [Member] \| Canada [Member]
Segment Reporting Information [Line Items]
Assets	71	80
Midstream Services [Member]
Segment Reporting Information [Line Items]
Revenues	273	317
Operating income (loss)	88	83
Depreciation, depletion and amortization	15	14
Interest expense	7	4
Provision (benefit) for income taxes	31	31
Assets	1,616	1,544
Capital investments	138	39
Midstream Services [Member] \| Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(665)	(913)
Other [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	(1)
Other income (loss), net		(1)
Gain (loss) on derivatives	(1)
Interest expense	(1)
Assets	268	258
Capital investments	3	4
Other [Member] \| Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(1)
Marketing [Member] \| Midstream Services [Member] \| Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(576)	(824)
WPX and Statoil Property Acquisitions [Member] \| Exploration and Production [Member]
Segment Reporting Information [Line Items]
Capital investments	534
WPX Property Acquisition [Member] \| Midstream Services [Member]
Segment Reporting Information [Line Items]
Capital investments	$ 119

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