Investment in and Advances to Unconsolidated Affiliates Affiliate Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Investments in and Advances to Affiliates, Affiliate Balance Sheet [Abstract]
Current assets	$ 74.5	$ 64.5
Property and equipment, net	233.9	234.6
Other assets, net	237.1	236.5
Total assets	545.5	535.6
Current liabilities	101.2	100.3
Long-term debt	114.7	110.1
Other liabilities	0.0	0.1
Members' equity	329.6	325.1
Total liabilities and members' equity	$ 545.5	$ 535.6