Consolidated Statement of Operations (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 4.76	$ 0.39	$ (6.85)
Income (Loss) from Discontinued Operations, Net of Tax, Per Basic Share	$ 1.83	$ 0.55	$ (1.95)
Earnings (Loss) Per Share, Basic	$ 6.59	$ 0.94	$ (8.80)
Income (Loss) from Continuing Operations, Per Diluted Share	$ 4.71	$ 0.39	$ (6.85)
Income (Loss) from Discontinued Operations, Net of Tax, Per Diluted Share	$ 1.81	$ 0.55	$ (1.95)
Earnings (Loss) Per Share, Diluted	$ 6.52	$ 0.94	$ (8.80)
Operating expenses:
Depreciation, depletion and amortization	$ 903	$ 930	$ 955
Ceiling test impairment	0	0	1,488
Other income (expenses):
Commodity derivative income (expense)	610	(97)	120
Income (loss) before income taxes	1,032	201	(1,374)
Income tax provision (benefit):
Total income tax provision (benefit)	382	128	(452)
Income (Loss) from Continuing Operations Attributable to Parent	650	73	(922)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	250	74	(262)
Net income (loss)	900	147	(1,184)
Weighted-average number of shares outstanding for basic earnings (loss) per share	137	135	135
Weighted average number of shares outstanding for diluted earnings (loss) per share	138	136	135
Continuing Operations [Member]
Statement [Line Items]
Oil, gas and NGL revenues	2,288	1,857	1,562
Operating expenses:
Lease operating	321	284	306
Gas Gathering, Transportation, Marketing and Processing Costs	174	137	107
Production and other taxes	111	79	85
Depreciation, depletion and amortization	870	685	704
General and administrative	222	219	211
Ceiling test impairment	0	0	1,488
Other	15	3	15
Total operating expenses	1,713	1,407	2,916
Income (loss) from operations	575	450	(1,354)
Other income (expenses):
Interest expense	(200)	(205)	(205)
Interest Costs Capitalized Adjustment	53	53	68
Commodity derivative income (expense)	610	(97)	120
Other	(6)	0	(3)
Total other income (expenses)	457	(249)	(20)
Income (loss) before income taxes	1,032	201	(1,374)
Income tax provision (benefit):
Current	5	(2)	16
Deferred	377	130	(468)
Total income tax provision (benefit)	$ 382	$ 128	$ (452)