Intangible Assets Schedule of Intangible Assets and Excess Reorganization Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	$ 123.5	$ 123.5
Accumulated intangible asset amortization	(40.8)	(30.2)
Amortizable intangible assets, net	$ 82.7	93.3
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	(25.9)	(19.9)
Amortizable intangible assets, net	28.7	34.7
Customer-Related Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Amortizable intangible assets, gross	68.9	68.9
Accumulated intangible asset amortization	(14.9)	(10.3)
Amortizable intangible assets, net	$ 54.0	$ 58.6