Valuation of Investments and Financial Instrument Assets Liabilities By Pricing Levels (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Money market fund investments	$ 236	$ 320
Deferred Compensation Plan Assets	6	6
Available-for-sale Securities	11	9
Obligations, Fair Value Disclosure	12	11
Total	249	299
Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Oil and gas derivative contracts	71	50
Commodity Option [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	(63)	(75)
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Money market fund investments	236	320
Deferred Compensation Plan Assets	6	6
Available-for-sale Securities	11	9
Obligations, Fair Value Disclosure	12	11
Total	241	324
Fair Value, Inputs, Level 1 [Member] \| Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Oil and gas derivative contracts		0
Derivative Liability	0
Fair Value, Inputs, Level 1 [Member] \| Commodity Option [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Oil and gas derivative contracts	0	0
Significant Other Observable Fair Value Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Money market fund investments	0	0
Deferred Compensation Plan Assets	0	0
Available-for-sale Securities	0	0
Obligations, Fair Value Disclosure	0	0
Total	71	50
Significant Other Observable Fair Value Inputs (Level 2) [Member] \| Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Oil and gas derivative contracts	71	50
Significant Other Observable Fair Value Inputs (Level 2) [Member] \| Commodity Option [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Oil and gas derivative contracts	0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Money market fund investments	0	0
Deferred Compensation Plan Assets	0	0
Available-for-sale Securities	0	0
Obligations, Fair Value Disclosure	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	(63)	(75)
Fair Value, Inputs, Level 3 [Member] \| Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Oil and gas derivative contracts		0
Derivative Liability	0
Fair Value, Inputs, Level 3 [Member] \| Commodity Option [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Liability	$ (63)	$ (75)

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