Segment Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating expenses:
Depreciation, depletion and amortization									$ 572	$ 917	$ 903
Impairment of Oil and Gas Properties	$ 0	$ 0	$ 522	$ 506	$ 702	$ 1,889	$ 1,521	$ 792	1,028	4,904	0
Allocated income tax (benefit)									22	(1,585)	382
Commodity derivative income (expense)									191	(259)	(610)
Income (loss) before income taxes									(1,208)	(4,947)	1,032
Total assets	4,312				4,768				4,312	4,768	9,580
Additions to long-lived assets									1,304	1,538	2,193
UNITED STATES
Segment Information [Line Items]
Oil, gas and NGL revenues									1,255	1,295	2,249
Operating expenses:
Lease operating									189	231	299
Transportation and processing									272	212	174
Production and other taxes									41	45	105
Depreciation, depletion and amortization									458	754	857
General and administrative									205	237	221
Impairment of Oil and Gas Properties									962	4,786
Other									20	9	25
Allocated income tax (benefit)									(330)	(1,842)	210
Net income (loss) from oil and gas properties									(562)	(3,137)	358
Total assets	4,166				4,452				4,166	4,452	8,852
Additions to long-lived assets									1,304	1,521	2,037
China [Member]
Segment Information [Line Items]
Oil, gas and NGL revenues									217	262	39
Operating expenses:
Lease operating									55	54	12
Transportation and processing									0	0	0
Production and other taxes									1	1	6
Depreciation, depletion and amortization									114	163	13
General and administrative									8	7	1
Impairment of Oil and Gas Properties									66	118
Other									0	1	0
Allocated income tax (benefit)									(16)	(49)	5
Net income (loss) from oil and gas properties									(11)	(33)	2
Total assets	$ 146				$ 316				146	316	728
Additions to long-lived assets									0	17	156
Continuing Operations [Member]
Segment Information [Line Items]
Oil, gas and NGL revenues									1,472	1,557	2,288
Operating expenses:
Lease operating									244	285	311
Transportation and processing									272	212	174
Production and other taxes									42	46	111
Depreciation, depletion and amortization									572	917	870
General and administrative									213	244	222
Impairment of Oil and Gas Properties									1,028	4,904
Other									20	10	25
Total operating expenses									2,391	6,618	1,713
Income (loss) from operations									(919)	(5,061)	575
Interest expenses, net of interest income, capitalized interest and other									(98)	(145)	(153)
Commodity derivative income (expense)									191	(259)	(610)
Income (loss) before income taxes									$ (1,208)	$ (4,947)	$ 1,032