Pension and Other Benefits Amounts Recognized in Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension and other postretirement benefits	$ 74.5	$ 77.5
Accumulated other comprehensive income (loss), defined benefit plan, gain (loss), after tax	38.6	36.9
Accumulated other comprehensive (income) loss, defined benefit plan, prior service cost (credit), after tax	0.1	0.1
Accumulated other comprehensive (income) loss, defined benefit plan, after tax	38.7	37.0
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension and other postretirement benefits	73.9	76.8
Accumulated other comprehensive income (loss), defined benefit plan, gain (loss), after tax	38.2	36.5
Accumulated other comprehensive (income) loss, defined benefit plan, prior service cost (credit), after tax	0.1	0.1
Accumulated other comprehensive (income) loss, defined benefit plan, after tax	38.3	36.6
Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension and other postretirement benefits	0.6	0.7
Accumulated other comprehensive income (loss), defined benefit plan, gain (loss), after tax	0.4	0.4
Accumulated other comprehensive (income) loss, defined benefit plan, prior service cost (credit), after tax	0.0	0.0
Accumulated other comprehensive (income) loss, defined benefit plan, after tax	$ 0.4	$ 0.4