Revenues Disaggregation of Revenue (Details) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segments	Jun. 30, 2017 USD ($)
Disaggregation of Revenue [Line Items]
Number of Reportable Segments | segments				1
Revenues from Contracts with Customers, Excluding Assessed Tax		$ 281.1		$ 612.2
Other operating revenues	[1]	4.2		8.5
Total operating revenues		285.3	$ 317.6	620.7	$ 684.6
Firm Service
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers, Excluding Assessed Tax	[2]	267.5		586.4
Interruptible Service
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers, Excluding Assessed Tax		7.8		17.3
Other revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers, Excluding Assessed Tax		$ 5.8		$ 8.5

[1] Other operating revenues include certain revenues earned from operating leases, pipeline management fees and other activities that are not considered central and ongoing major business operations of the Partnership and do not represent revenues earned from contracts with customers.

[2] Revenues earned from contracts with MVCs are included in firm service given the stand-ready nature of the performance obligation and the guaranteed nature of the fees over the contract term.