Acquisitions & Divestitures (Schedule Of Purchase Accounting Entries) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014
Significant Acquisitions and Disposals [Line Items]
Payments to Acquire Businesses, Gross	$ 945.0
Fair value of assets acquired (liabilities assumed)	945.0
Proved Property [Member]
Significant Acquisitions and Disposals [Line Items]
Fair value of assets acquired (liabilities assumed)	516.1
Unproved Property [Member]
Significant Acquisitions and Disposals [Line Items]
Fair value of assets acquired (liabilities assumed)	439.7
Asset Retirement Obligation Costs [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)	(1.1)
Permian Basin [Member]
Significant Acquisitions and Disposals [Line Items]
Payments to Acquire Businesses, Gross	$ 945.0