Income Taxes Schedule of Deferred Tax Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Deferred Tax Assets and Liabilities [Abstract]
Deferred Tax Liabilities,Natural Gas and Oil Properties	$ (1,999)	$ (2,883)
Deferred Tax Liabilities, Other Property and Equipment	(436)	(634)
Deferred Tax Liabilities, Investments	0	(56)
Deferred Tax Liabilities, Volumetric Production Payments	(1,432)	(1,453)
Deferred Tax Liabilities, Contingent Convertible Debt	(416)	(396)
Deferred Tax Liabilities, Gross	(4,283)	(5,422)
Deferred Tax Assets, Net Operating Loss Carryforwards	414	1,198
Deferred Tax Assets, Derivative Instruments	172	395
Deferred Tax Assets, Asset Retirement Obligations	142	123
Deferred Tax Assets, Investments	106	0
Deferred Tax Assets, Deferred Stock Compensation	47	62
Deferred Tax Assets, Accrued Liabilities	90	82
Deferred Tax Assets, Noncontrolling Interests	178	114
Deferred Tax Assets, Alternative Minimum Tax Credits	225	257
Deferred Tax Assets, State Statutory Depletion	137	121
Deferred Tax Assets, Other	55	(29)
Deferred Tax Assets	1,566	2,323
Deferred Tax Assets, Net	(2,717)	(3,099)
Other Non-Current Tax Liabilities	0	(246)
Deferred Tax Liabilities, Net	(2,717)	(3,345)
Deferred income tax asset	90	139
Deferred income tax liabilities	$ (2,807)	$ (3,484)