Consolidated Statement of Operations (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Per Basic Share	$ 2.04	$ (0.03)	$ 2.06	$ 0.57
Income (Loss) from Discontinued Operations, Net of Tax, Per Basic Share	$ 0.00	$ 0.08	$ 1.90	$ 0.24
Earnings (Loss) Per Share, Basic	$ 2.04	$ 0.05	$ 3.96	$ 0.81
Income (Loss) from Continuing Operations, Per Diluted Share	$ 2.02	$ (0.03)	$ 2.04	$ 0.57
Income (Loss) from Discontinued Operations, Net of Tax, Per Diluted Share	$ 0.00	$ 0.08	$ 1.88	$ 0.24
Earnings (Loss) Per Share, Diluted	$ 2.02	$ 0.05	$ 3.92	$ 0.81
Weighted-average number of shares outstanding for basic earnings (loss) per share	137	136	137	135
Weighted average number of shares outstanding for diluted earnings (loss) per share	138	136	138	136
Operating expenses:
Depreciation, depletion and amortization			$ 665	$ 664
Other income (expenses):
Interest expense	(51)	(52)	(153)	(153)
Interest Costs Capitalized Adjustment	13	13	39	40
Commodity derivative income (expense)	303	(99)	33	(66)
Other	1	1	4	5
Total other income (expenses)	266	(137)	(77)	(174)
Income (loss) before income taxes	435	(6)	445	124
Income tax provision (benefit):
Current	1	(4)	1	(4)
Deferred	155	2	164	51
Total income tax provision (benefit)	156	(2)	165	47
Income (Loss) from Continuing Operations Attributable to Parent	279	(4)	280	77
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	(1)	31	260	53
Net income (loss)	278	27	540	130
Segment, Continuing Operations [Member]
Statement [Line Items]
Oil, gas and NGL revenues	610	486	1,771	1,291
Operating expenses:
Lease operating	126	104	356	299
Production and other taxes	31	19	85	52
Depreciation, depletion and amortization	228	171	628	482
General and administrative	48	61	172	160
Other	8	0	8	0
Total operating expenses	441	355	1,249	993
Income (loss) from operations	$ 169	$ 131	$ 522	$ 298