Consolidated Statements of Operations (unaudited) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues
Oil, Gas and NGL Sales	$ 1,341	$ 954	$ 3,537	$ 2,925
Income from Equity Method Investees	53	51	150	137
Total	1,394	1,005	3,687	3,062
Costs and Expenses
Production Expense	221	158	619	492
Exploration Expense	60	95	211	322
Depreciation, Depletion and Amortization	412	368	1,146	987
General and Administrative	109	93	324	286
Gain on Divestitures	0	(157)	(12)	(167)
Asset Impairments	63	0	63	73
Other Operating (Income) Expense, Net	6	(2)	27	19
Total	871	555	2,378	2,012
Operating Income	523	450	1,309	1,050
Other (Income) Expense
(Gain) Loss on Commodity Derivative Instruments	157	135	69	(46)
Interest, Net of Amount Capitalized	46	36	104	95
Other Non-Operating (Income) Expense, Net	9	4	21	2
Total	212	175	194	51
Income from Continuing Operations Before Income Taxes	311	275	1,115	999
Income Tax Provision	116	111	330	312
Income from Continuing Operations	195	164	785	687
Discontinued Operations, Net of Tax	10	57	58	89
Net Income	$ 205	$ 221	$ 843	$ 776
Earnings Per Share, Basic [Abstract]
Income from Continuing Operations (in dollars per share)	$ 0.54	$ 0.46	$ 2.19	$ 1.93
Discontinued Operations, Net of Tax (in dollars per share)	$ 0.03	$ 0.16	$ 0.16	$ 0.25
Net Income (in dollars per share)	$ 0.57	$ 0.62	$ 2.35	$ 2.18
Earnings Per Share, Diluted [Abstract]
Income from Continuing Operations (in dollars per share)	$ 0.53	$ 0.45	$ 2.17	$ 1.90
Discontinued Operations, Net of Tax (in dollars per share)	$ 0.03	$ 0.16	$ 0.16	$ 0.25
Net Income (in dollars per share)	$ 0.56	$ 0.61	$ 2.33	$ 2.15
Weighted Average Number of Shares Outstanding [Abstract]
Weighted Average Number of Shares Outstanding, Basic (in shares)	359	356	359	356
Weighted Average Number of Shares Outstanding, Diluted (in shares)	363	359	363	361