Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Current income tax provision	$ 1.0	$ 1.2
Deferred income tax provision	0.8	5.8
Income tax provision	1.8	7.0
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Expected income tax provision (benefit) based on federal statutory rate	(36.7)	4.1
State income tax provision (benefit), net of federal benefit	(4.4)	0.5
Income tax provision from ENLK	0.9	1.0
Unit-based compensation	0.1	1.6
Non-deductible expense related to asset impairment	43.8	0.0
Other	(1.9)	(0.2)
Income tax provision	1.8	7.0
Deferred income tax assets:
Federal net operating loss carryforward	77.4		$ 67.9
State net operating loss carryforward	13.1		11.7
Total deferred tax assets	90.5		79.6
Deferred tax liabilities:
Property, equipment, and intangible assets	(54.0)		(440.6)
Other	(0.3)		(1.4)
Total deferred tax liabilities	54.3		442.0
Deferred Tax Liabilities, Net			(362.4)
Deferred Tax Assets, Net	36.2
Issuance of common units for ENLK public common units related to the Merger	399.0	$ 0.9
Domestic Tax Authority
Deferred tax liabilities:
Operating loss carryforwards	368.5		323.6
State and Local Jurisdiction
Deferred tax liabilities:
Deferred Tax Assets, Net	$ 77.4		$ 67.9