Asset Retirement Obligations (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset retirement obligation, current		$ 1.9	$ 1.3
Asset retirement obligations, noncurrent		204.9	193.8
ARO Liability [Roll Forward]
ARO liability, Beginning Balance	[1]	195.1	165.1
Accretion		8.7	6.7
Liabilities incurred	[2]	3.8	17.1
Revisions of Estimates		17.2	33.6
ARO Liabilities Transferred		(16.0)	(24.7)
Liabilities settled		(2.0)	(2.7)
ARO liability, Ending Balance		$ 206.8	195.1	[1]
Midstream Business Held For Sale [Member] | Asset Retirement Obligation Costs [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset retirement obligations, noncurrent			28.5
Permian Basin Acquisition [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Recognized identifiable assets acquired and liabilities assumed, net			941.8
Permian Basin Acquisition [Member] | Asset Retirement Obligation Costs [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Recognized identifiable assets acquired and liabilities assumed, net			$ 9.7

[1] Excludes $28.5 million of ARO as of January 1, 2014, classified as "Noncurrent liabilities of discontinued operations" on the Consolidated Balance Sheet.

[2] Additions for the year ended December 31, 2014, include $9.7 million related to the Permian Basin Acquisition (see Note 2 – Acquisitions and Divestitures).