Fair Value Measurements and Disclosures - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Financial Assets
Mutual Fund Investments	$ 67	$ 71
Commodity Derivative Instruments	31	0
Financial Liabilities
Commodity Derivative Instruments	0	(116)
Portion of Deferred Compensation Liability Measured at Fair Value	(86)	(88)
Stock Based Compensation Liability Measured at Fair Value	(12)	(9)
Quoted Prices in Active Markets (Level 1)
Financial Assets
Mutual Fund Investments	67	71
Commodity Derivative Instruments	0	0
Financial Liabilities
Commodity Derivative Instruments	0	0
Portion of Deferred Compensation Liability Measured at Fair Value	(86)	(88)
Stock Based Compensation Liability Measured at Fair Value	(12)	(9)
Significant Other Observable Inputs (Level 2)
Financial Assets
Mutual Fund Investments	0	0
Commodity Derivative Instruments	34	5
Financial Liabilities
Commodity Derivative Instruments	(3)	(121)
Portion of Deferred Compensation Liability Measured at Fair Value	0	0
Stock Based Compensation Liability Measured at Fair Value	0	0
Significant Unobservable Inputs (Level 3)
Financial Assets
Mutual Fund Investments	0	0
Commodity Derivative Instruments	0
Financial Liabilities
Commodity Derivative Instruments	0	0
Portion of Deferred Compensation Liability Measured at Fair Value	0	0
Stock Based Compensation Liability Measured at Fair Value	0	0
Scenario, Adjustment
Financial Assets
Mutual Fund Investments	0	0
Commodity Derivative Instruments	(3)	(5)
Financial Liabilities
Commodity Derivative Instruments	3	5
Portion of Deferred Compensation Liability Measured at Fair Value	0	0
Stock Based Compensation Liability Measured at Fair Value	$ 0	$ 0