Other Operating (Income) Expense (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Other Income And Expenses [Abstract]
(Gain) loss on sale or disposition of assets	[1]	$ (0.1)	$ 16.1
Miscellaneous business tax		0.3	0.1
Other		0.1
Total other operating (income) expense		$ 0.3	$ 16.2

[1] Comprised primarily of a $16.1 million loss in the first quarter of 2017 due to the reduction in the carrying value of our ownership interest in VGS in connection with the April 4, 2017 sale.