Investment in and Advances to Unconsolidated Affiliates Affiliate Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Investments in and Advances to Affiliates, Affiliate Balance Sheet [Abstract]
Current assets	$ 71.1	$ 64.5
Property and equipment, net	231.0	234.6
Other assets, net	241.0	236.5
Total assets	543.1	535.6
Current liabilities	96.8	100.3
Long-term debt	104.6	110.1
Other liabilities	1.2	0.1
Members' equity	340.5	325.1
Total liabilities and members' equity	$ 543.1	$ 535.6