Goodwill and Intangible Assets, Identifiable Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Identifiable intangible assets
Net book value		$ 25.0	$ 26.4
Impairment of Intangible Assets	$ 2.6
Amortization of definite-lived intangible assets		1.4	1.5	$ 1.6
Impairment of the carrying value of goodwill		18.4	0.0	$ 0.0
Expected amortization of intangible assets for the next five years
2018		1.4
2019		1.4
2020		1.4
2021		1.4
2022		1.4
Expected amortization of intangible assets, after 2022		18.0
Customer relationships
Identifiable intangible assets
Original cost		34.7	34.7
Accumulated amortization		(9.7)	(8.3)
Net book value		$ 25.0	$ 26.4