Employees - Financial Information Related to Pension Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 131.0	$ 146.9
Service cost	0.0	0.4	$ 1.2
Interest cost	5.4	5.2	2.7
Actuarial loss (gain)	13.6	(9.9)
Benefits paid	(5.3)	(9.1)
Other (effect of curtailment/settlement)	(13.2)	(2.5)
Projected benefit obligations at end of year	131.5	131.0	146.9
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	115.7	108.8
Actual gain (loss) on plan assets	29.5	(8.2)
Employer contribution	1.4	24.2
Benefits paid	(5.3)	(9.1)
Other (effect of curtailment/settlement)	(13.2)	0.0
Fair value of plan assets at end of year	128.1	115.7	$ 108.8
Under-funded status at end of year	$ (3.4)	$ (15.3)