Acquisitions & Divestitures (Narrative) (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	4 Months Ended	6 Months Ended		3 Months Ended	6 Months Ended
	Aug. 14, 2013	Jun. 30, 2014 acre	Jun. 30, 2014 acre	Jun. 30, 2014 Term Loan due 2017 [Member]	Jun. 30, 2014 Permian Basin [Member]	Jun. 30, 2014 Permian Basin [Member]
Business Acquisition [Line Items]
Liabilities incurred			$ 13.2			$ 9.7
Aggregate sale price of assets disposed		702.3	702.3
Pretax loss on sale of assets		200.9	200.9
Consideration Held In Escrow Pending Title Defects		28.7	28.7
Payments to Acquire Businesses, Gross			945.0		942.1
Business Combination Consideration Receivable			(2.9)
Payments to Acquire Businesses Net			942.1
Net acres of producing and undeveloped oil and gas properties		26,500	26,500
Number of vertical producing wells		270	270
Escrow Deposit		50.0	50.0
Borrowings to Fund Acquisition				300.0
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual		61.9
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual		14.0
Business Acquisition, Transaction Costs		0.6	0.6
Debt Issuance Cost	$ 3.0		$ 1.1