Employee Benefit Plans - Rollforward of Unobservable Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation
Fair value of plan assets at beginning of year	$ 49.1	$ 42.8
Fair value of plan assets at year end	53.9	49.1
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation
Fair value of plan assets at beginning of year	0.3	0.2
Purchases, sales and settlements, net	(3.0)	(3.1)
Transfers, net	4.5	3.2
Fair value of plan assets at year end	$ 1.8	$ 0.3