Segment Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues	$ 687	$ 749	$ 764	$ 933	$ 962	$ 928	$ 1,035	$ 1,113	$ 3,133	$ 4,038	$ 3,371
Operating income (loss)	(2,561)	(2,842)	(1,284)	$ 165	285	$ 286	$ 367	$ 435	(6,522)	1,373	1,204
Other income (loss), net									(30)	(4)	2
Gain (loss) on derivatives									47	139	26
Depreciation, depletion and amortization expense									1,091	942	787
Impairment of natural gas and oil properties	2,600	$ 2,800	$ 1,500						6,950
Interest expense									56	59	42
Provision (benefit) for income taxes									(2,005)	525	486
Assets	8,110				14,925				8,110	14,925	8,048
Capital investments									2,437	7,447	2,235
Impairment of natural gas and oil properties									6,950
Change in accrued expenditures									(33)	155	(25)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues									(2,060)	(3,182)	(2,380)
Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenues									2,095	2,850	2,398
Operating income (loss)									(7,104)	1,013	879
Other income (loss), net									(21)	(3)	3
Gain (loss) on derivatives									51	142	26
Depreciation, depletion and amortization expense									1,028	884	735
Impairment of natural gas and oil properties									6,950
Interest expense									47	47	30
Provision (benefit) for income taxes									(2,273)	402	368
Assets	6,588				13,018				6,588	13,018	6,357
Capital investments									2,258	7,254	2,052
Exploration and Production [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues									21	(12)	(6)
Exploration and Production [Member] | Canada [Member]
Segment Reporting Information [Line Items]
Assets	50				77				50	77	79
Capital investments									4	11	35
Midstream Services [Member]
Segment Reporting Information [Line Items]
Revenues									1,038	1,188	973
Operating income (loss)									583	361	325
Other income (loss), net									(9)	(1)
Gain (loss) on derivatives										(1)
Depreciation, depletion and amortization expense									62	58	51
Interest expense									9	12	11
Provision (benefit) for income taxes									268	123	119
Assets	1,290				1,554				1,290	1,554	1,427
Capital investments									167	144	158
Midstream Services [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues									(2,081)	(3,170)	(2,374)
Other [Member]
Segment Reporting Information [Line Items]
Operating income (loss)									(1)	(1)
Other income (loss), net											(1)
Gain (loss) on derivatives									(4)	(2)
Depreciation, depletion and amortization expense									1		1
Interest expense											1
Provision (benefit) for income taxes											(1)
Assets	$ 232				$ 353				232	353	264
Capital investments									12	49	25
Marketing [Member] | Midstream Services [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues									$ (1,800)	$ (2,800)	$ (2,000)