Merger, Acquisitions and Divestitures - Sales Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Proceeds from Divestitures	$ 151	$ 321	$ 327
Asset Retirement Obligations Associated with Assets Sold	38	101
Gain on Divestitures	0	73	36
US Onshore Assets Sold
Business Acquisition [Line Items]
Proceeds from Divestitures	151	135	150
Net Book Value of Assets Sold	(156)	(150)	(117)
Goodwill Allocated to Assets Sold	(4)	(7)	(8)
Asset Retirement Obligations Associated with Assets Sold	8	48	8
Other Closing Adjustments	1	10	3
Gain on Divestitures	0	$ 36	$ 36
China
Business Acquisition [Line Items]
Proceeds from Divestitures	186
Net Book Value of Assets Sold	(149)
Other Closing Adjustments	2
Gain on Divestitures	$ (35)