Leases - Lease Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Leases [Abstract]
Operating lease costs	$ 5.1		$ 15.3
Variable lease costs	0.0		2.1
Sublease income	(0.1)		(0.3)
Total lease costs	$ 5.0	$ 5.2	17.1	$ 18.2
Operating cash flows from operating leases (fixed payments)			14.1
Operating cash flows from operating leases (liability reduction)			$ 11.5