Merger, Acquisitions and Divestitures - Discontinued Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operations, Net of Tax	$ 0	$ 0	$ 71
North Sea Assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Oil and Gas Sales			37
Income Before Income Taxes			12
Income Tax Expense			6
Operating Income, Net of Tax			6
Gain on Sale, Net of Tax			$ 65