Consolidated Statements of Operations (unaudited) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Revenues
Oil, Gas and NGL Sales	$ 1,112	$ 934	$ 2,196	$ 1,970
Income from Equity Method Investees	37	31	96	83
Total	1,149	965	2,292	2,053
Costs and Expenses
Production Expense	210	168	398	331
Exploration Expense	90	167	151	227
Depreciation, Depletion and Amortization	368	325	734	619
General and Administrative	104	96	216	193
Other Operating Expense, Net	16	71	8	83
Total	788	827	1,507	1,453
Operating Income	361	138	785	600
Other (Income) Expense
Gain on Commodity Derivative Instruments	(161)	(276)	(89)	(180)
Interest, Net of Amount Capitalized	33	27	58	59
Other Non-Operating (Income) Expense, Net	3	(3)	12	(3)
Total	(125)	(252)	(19)	(124)
Income from Continuing Operations Before Income Taxes	486	390	804	724
Income Tax Provision	128	115	214	200
Income from Continuing Operations	358	275	590	524
Discontinued Operations, Net of Tax	19	17	49	32
Net Income	$ 377	$ 292	$ 639	$ 556
Earnings Per Share, Basic [Abstract]
Income from Continuing Operations (in dollars per share)	$ 1.00	$ 0.77	$ 1.64	$ 1.47
Discontinued Operations, Net of Tax (in dollars per share)	$ 0.05	$ 0.05	$ 0.14	$ 0.09
Net Income (in dollars per share)	$ 1.05	$ 0.82	$ 1.78	$ 1.56
Earnings Per Share, Diluted [Abstract]
Income from Continuing Operations (in dollars per share)	$ 0.99	$ 0.74	$ 1.63	$ 1.44
Discontinued Operations, Net of Tax (in dollars per share)	$ 0.05	$ 0.05	$ 0.13	$ 0.09
Net Income (in dollars per share)	$ 1.04	$ 0.79	$ 1.76	$ 1.53
Weighted Average Number of Shares Outstanding, Basic (in shares)	359	356	358	355
Weighted Average Number of Shares Outstanding, Diluted (in shares)	363	361	362	360