Investment in and Advances to Unconsolidated Affiliates Affiliate Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Investments in and Advances to Affiliates, Affiliate Balance Sheet [Abstract]
Current assets	$ 21.5	$ 64.5
Property and equipment, net	98.0	234.6
Other assets, net	107.0	236.5
Total assets	226.5	535.6
Current liabilities	19.3	100.3
Long-term debt	1.6	110.1
Other liabilities	0.1	0.1
Members' equity	205.5	325.1
Total liabilities and members' equity	$ 226.5	$ 535.6