Discontinued Operations (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Value of midstream business sold	$ 2,500,000,000		$ 2,500,000,000
Debt refinancing included in sale of midstream business	230,000,000		230,000,000
Continuing cash flows related to midstream business held for sale	19,000,000	25,900,000	64,100,000	67,200,000
Depreciation, depletion and amortization	251,400,000	238,400,000	712,500,000	719,300,000
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	14,300,000	14,700,000	43,100,000	37,800,000
Property, plant and equipment, including dry exploratory well expense			$ 45,600,000	$ 57,400,000