Acquisitions and Divestitures Terminated Williston Basin Divestiture (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment	$ 678.9	$ 243.6	$ 806.8
Williston Basin Divestiture [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Definitive Agreement Agreed Upon Sales Price		1,725.0
Cash and Contractual Rights		1,650.0
Rights To Acquire Common Stock		$ 75.0