Discontinued Operations (Narrative) (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]
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	$ 131.8	145.3	$ 124.6
Depreciation, depletion and amortization	$ 881.1	994.7	963.8
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	52.2
Payments to Acquire Oil and Gas Property and Equipment		$ 55.2	$ 88.9