Employee Benefit Plans - Change in Level 3 Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Change in fair value of the pension assets valued using significant unobservable inputs (Level 3)
Fair value of plan assets at beginning of year	$ 115.5	$ 99.3
Fair value of assets at end of year	106.9	115.5
Level 3
Change in fair value of the pension assets valued using significant unobservable inputs (Level 3)
Fair value of plan assets at beginning of year	4.2	10.9
Unrealized gain (loss) on asset still held	0.0	(6.7)
Fair value of assets at end of year	$ 4.2	$ 4.2