Fair Value Measurements and Disclosures of Assets and Liabilities Measured on a Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Financial Assets [Abstract]
Mutual Fund Investments	$ 116		$ 114
Commodity Derivative Instruments	11		17
Financial Liabilities [Abstract]
Commodity Derivative Instruments	(111)		(75)
Portion of Deferred Compensation Liability Measured at Fair Value	(181)		(176)
Quoted Prices in Active Markets (Level 1)
Financial Assets [Abstract]
Mutual Fund Investments	116	[1]	114	[1]
Commodity Derivative Instruments	0		0
Financial Liabilities [Abstract]
Commodity Derivative Instruments	0		0
Portion of Deferred Compensation Liability Measured at Fair Value	(181)	[1]	(176)	[1]
Significant Other Observable Inputs (Level 2)
Financial Assets [Abstract]
Mutual Fund Investments	0		0
Commodity Derivative Instruments	15	[2]	28	[2]
Financial Liabilities [Abstract]
Commodity Derivative Instruments	(115)	[2]	(86)	[2]
Portion of Deferred Compensation Liability Measured at Fair Value	0		0
Significant Unobservable Inputs (Level 3)
Financial Assets [Abstract]
Mutual Fund Investments	0		0
Commodity Derivative Instruments	0		0
Financial Liabilities [Abstract]
Commodity Derivative Instruments	0		0
Portion of Deferred Compensation Liability Measured at Fair Value	0		0
Adjustment
Financial Assets [Abstract]
Mutual Fund Investments	0		0
Commodity Derivative Instruments	(4)	[3]	(11)	[3]
Financial Liabilities [Abstract]
Commodity Derivative Instruments	4	[3]	11	[3]
Portion of Deferred Compensation Liability Measured at Fair Value	$ 0		$ 0

[1] Level 1 measurements are fair value measurements which use quoted market prices (unadjusted) in active markets for identical assets or liabilities. We use Level 1 inputs when available as Level 1 inputs generally provide the most reliable evidence of fair value.

[2] Level 2 measurements are fair value measurements which use inputs, other than quoted prices included within Level 1, which are observable for the asset or liability, either directly or indirectly.

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