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Acquisitions & Divestitures (Schedule Of Purchase Accounting Entries) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Significant Acquisitions and Disposals [Line Items]
Payments to Acquire Businesses Net			$ 941.8
Fair value of assets acquired (liabilities assumed)			941.8
Proved Property [Member]
Significant Acquisitions and Disposals [Line Items]
Fair value of assets acquired (liabilities assumed)			472.1
Unproved Property [Member]
Significant Acquisitions and Disposals [Line Items]
Fair value of assets acquired (liabilities assumed)			480.6
Asset Retirement Obligation [Member]
Significant Acquisitions and Disposals [Line Items]
Fair value of assets acquired (liabilities assumed)			(9.7)
Other Liabilities [Member]
Significant Acquisitions and Disposals [Line Items]
Fair value of assets acquired (liabilities assumed)			(1.2)
Permian Basin [Member]
Significant Acquisitions and Disposals [Line Items]
Payments to Acquire Businesses, Gross			941.8
Southern Region Divestitures [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Disposition of Oil and Gas and Timber Property	$ (1.1)	$ (2.9)	53.3
Midcontinent Divestitures [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Disposition of Oil and Gas and Timber Property	$ 0.4	$ (26.4)	$ (199.4)