Fair Value Measurements and Disclosures of Assets and Liabilities Measured on a Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Financial Assets [Abstract]
Mutual Fund Investments	$ 103		$ 99
Commodity Derivative Investments	84		47
Financial Liabilities [Abstract]
Commodity Derivative Instruments	(10)		(83)
Portion of Deferred Compensation Liability Measured at Fair Value	(160)		(162)
Quoted Prices in Active Markets (Level 1)
Financial Assets [Abstract]
Mutual Fund Investments	103	[1]	99	[1]
Commodity Derivative Investments	0	[1]	0	[1]
Financial Liabilities [Abstract]
Commodity Derivative Instruments	0	[1]	0	[1]
Portion of Deferred Compensation Liability Measured at Fair Value	(160)	[1]	(162)	[1]
Significant Other Observable Inputs (Level 2)
Financial Assets [Abstract]
Mutual Fund Investments	0	[1]	0	[1]
Commodity Derivative Investments	113	[1]	99	[1]
Financial Liabilities [Abstract]
Commodity Derivative Instruments	(39)	[1]	(135)	[1]
Portion of Deferred Compensation Liability Measured at Fair Value	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3)
Financial Assets [Abstract]
Mutual Fund Investments	0	[1]	0	[1]
Commodity Derivative Investments	0	[1]	0	[1]
Financial Liabilities [Abstract]
Commodity Derivative Instruments	0	[1]	0	[1]
Portion of Deferred Compensation Liability Measured at Fair Value	0	[1]	0	[1]
Adjustment
Financial Assets [Abstract]
Mutual Fund Investments	0	[2]	0	[2]
Commodity Derivative Investments	(29)	[2]	(52)	[2]
Financial Liabilities [Abstract]
Commodity Derivative Instruments	29	[2]	52	[2]
Portion of Deferred Compensation Liability Measured at Fair Value	$ 0	[2]	$ 0	[2]

[1] See Note 1. Summary of Significant Accounting Policies - Fair Value Measurements for a description of the fair value hierarchy.

[2] Amount represents the impact of netting clauses within our master agreements that allow us to net cash settle asset and liability positions with the same counterparty.