Goodwill and Intangibles - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Finite-lived Intangible Assets Acquired	$ 0.0	$ 48.0	$ 0.0	$ 48.0
Finite-Lived Intangible Assets, Period Increase (Decrease)	0.0	(3.1)	0.0	(3.1)
Goodwill [Roll Forward]
CDI, net, beginning of period	47.3	9.0	49.1	9.6
CDI current period amortization	(1.7)	(1.1)	(3.5)	(1.7)
Total CDI, net, at September 30	$ 45.6	$ 52.8	$ 45.6	$ 52.8