Property, Plant and Equipment - Components of Property, Plant and Equipment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Sep. 30, 2018
Property Plant And Equipment [Line Items]
Land	$ 12.0		$ 11.0
Building and improvements	40.0		39.0
Pipeline and equipment	1,196.0		1,162.0
Other	18.0		18.0
Property, plant and equipment, gross	1,266.0		1,230.0
Accumulated depreciation and amortization	(579.0)		(567.0)
Property plant and equipment excluding construction in progress	687.0		663.0
Construction in progress	53.0		79.0
Property, plant and equipment, net	740.0		742.0
Operating leased assets, cost	366.0
Costs related to assets under capital lease	23.0		22.8
Accumulated depreciation on assets under operating lease	124.0		$ 121.0
Accumulated depreciation on assets under capital lease				$ 5.0
Depreciation and amortization expense	$ 12.0	$ 11.0
Building and Improvements | Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life	10 years
Building and Improvements | Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life	40 years
Pipeline and Equipment | Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life	10 years
Pipeline and Equipment | Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life	30 years
Other | Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life	5 years
Other | Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life	25 years