Acquisitions and Dispositions (Unaudited) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2014	Sep. 08, 2014	Jun. 20, 2014
Business Acquisition [Line Items]
Income Tax Expense (Benefit), Changes in Deferred Tax Liabilities and Deferred Tax Asset Valuation Allowances			$ 62.0
Eagle Ford [Member]
Business Acquisition [Line Items]
Disposal Date		Jun. 20, 2014
Business Combination, Consideration Transferred		$ 3,100.0
Effective Date		Apr. 01, 2014
Income Tax Expense (Benefit), Changes in Deferred Tax Liabilities and Deferred Tax Asset Valuation Allowances		$ 62.0
Adjustment to Goodwill		221.0
Escrow Deposit Disbursements Related to Property Acquisition					$ 1,300.0
Deepwater Gulf of Mexico Interests [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 496.0	$ 918.0
Effective Date	Sep. 08, 2014	Jun. 30, 2014
Escrow Deposit Disbursements Related to Property Acquisition				$ 414.0
Business Combination, Adjustment to Recognized Identifiable Assets Acquired and Liabilities Assumed Oil and Gas Properties Subject to Depletion	$ 509.0	$ 451.0
Business Combination, Adjustment to Recognized Identifiable Assets Acquired and Liabilities Assumed Oil and Gas Properties Not Subject to Depletion		477.0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Asset Retirement Costs		$ 10.0