Intangible Assets Schedule of Intangible Assets and Excess Reorganization Value (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	$ 123.5	$ 123.5
Accumulated intangible asset amortization	(42.2)	(40.8)
Amortizable intangible assets, net	$ 81.3	82.7
Average useful life of finite-lived intangible assets	15 years
Contract-Based Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	$ 54.6	54.6
Accumulated intangible asset amortization	(26.1)	(25.9)
Amortizable intangible assets, net	28.5	28.7
Customer-Related Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	68.9	68.9
Accumulated intangible asset amortization	(16.1)	(14.9)
Amortizable intangible assets, net	$ 52.8	$ 54.0