Fair Value Measurements and Disclosures of Assets and Liabilities Measured on a Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Financial Assets [Abstract]
Mutual Fund Investments	$ 111		$ 114
Commodity Derivative Investments	890		17
Financial Liabilities [Abstract]
Commodity Derivative Instruments	0		(75)
Portion of Deferred Compensation Liability Measured at Fair Value	(134)		(176)
Quoted Prices in Active Markets (Level 1)
Financial Assets [Abstract]
Mutual Fund Investments	111		114
Commodity Derivative Investments	0	[1]	0
Financial Liabilities [Abstract]
Commodity Derivative Instruments	0	[1]	0	[1]
Portion of Deferred Compensation Liability Measured at Fair Value	(134)		(176)	[1]
Significant Other Observable Inputs (Level 2)
Financial Assets [Abstract]
Mutual Fund Investments	0	[1]	0	[1]
Commodity Derivative Investments	890	[1]	28	[1]
Financial Liabilities [Abstract]
Commodity Derivative Instruments	0	[1]	(86)	[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	0	[2]	(11)	[2]
Financial Liabilities [Abstract]
Commodity Derivative Instruments	0	[2]	11	[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.