Discontinued Operations (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Value of business sold			$ 2,500.0
Debt refinanced in business sale			230.0
Pre-tax gain on sale of discontinued operations			1,800.0
Continuing Cash Flows To Business Held For Sale	$ 137.9	$ 131.8	145.3
Retention Bonuses Related To Discontinued Operations			10.4
Midstream Business Held For Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Depreciation, depletion and amortization			45.9
Payments to Acquire Oil and Gas Property and Equipment			$ 55.2