Fair Value Measurements and Disclosures of Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Financial Assets [Abstract]
Mutual Fund Investments		$ 77	$ 90
Commodity Derivative Instruments		460	592
Financial Liabilities [Abstract]
Commodity Derivative Instruments		(3)	0
Portion of Deferred Compensation Liability Measured at Fair Value		(96)	(98)
Fair Value Liabilities Measured on a Recurring Basis Stock Compensation Liability		(1)
Quoted Prices in Active Markets (Level 1)
Financial Assets [Abstract]
Mutual Fund Investments	[1]	77	90
Commodity Derivative Instruments	[1]	0	0
Financial Liabilities [Abstract]
Commodity Derivative Instruments	[1]	0	0
Portion of Deferred Compensation Liability Measured at Fair Value	[1]	(96)	(98)
Fair Value Liabilities Measured on a Recurring Basis Stock Compensation Liability	[1]	(1)
Significant Unobservable Inputs (Level 3)
Financial Assets [Abstract]
Mutual Fund Investments	[2]	0	0
Commodity Derivative Instruments	[2]	0	0
Financial Liabilities [Abstract]
Commodity Derivative Instruments	[2]	0	0
Portion of Deferred Compensation Liability Measured at Fair Value	[2]	0	0
Fair Value Liabilities Measured on a Recurring Basis Stock Compensation Liability	[2]	0
Significant Other Observable Inputs (Level 2)
Financial Assets [Abstract]
Mutual Fund Investments	[3]	0	0
Commodity Derivative Instruments	[3]	472	600
Financial Liabilities [Abstract]
Commodity Derivative Instruments	[3]	(15)	(8)
Portion of Deferred Compensation Liability Measured at Fair Value	[3]	0	0
Fair Value Liabilities Measured on a Recurring Basis Stock Compensation Liability	[3]	0
Scenario, Adjustment [Member]
Financial Assets [Abstract]
Mutual Fund Investments	[4]	0	0
Commodity Derivative Instruments	[4]	(12)	(8)
Financial Liabilities [Abstract]
Commodity Derivative Instruments	[4]	12	8
Portion of Deferred Compensation Liability Measured at Fair Value	[4]	0	$ 0
Fair Value Liabilities Measured on a Recurring Basis Stock Compensation Liability	[4]	$ 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 3 measurements are fair value measurements which use unobservable inputs.

[3] 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.

[4] 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.