Fair Value Measurements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2017
Liabilities:
Carrying value of debt, net of unamortized discount	$ 9,800	$ 9,800
Level 2
Liabilities:
Debt estimated fair value		225
Fair Value
Liabilities:
Debt estimated fair value	10,200	10,300
Recurring | Level 2 | Accrued liabilities
Liabilities:
Embedded derivative	43	54
Recurring | Level 2 | Deferred credits and other liabilities - other
Liabilities:
Embedded derivative	178	183
Recurring | Fair Value | Accrued liabilities
Liabilities:
Embedded derivative	43	54
Recurring | Fair Value | Deferred credits and other liabilities - other
Liabilities:
Embedded derivative	178	$ 183
Non recurring | Proved gas and oil properties
Liabilities:
Pre-tax Impairment Charges	$ 15