Pension and Postretirement Benefit Plans (Net Periodic Pension Costs Included in Accumulated Other Comprehensive Income (Loss)) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($)
Defined benefit plans
Before-Tax Amount
Accumulated other comprehensive loss, beginning of period	$ (302.4)
Accumulated other comprehensive, end of period	(300.0)
Income Tax
Accumulated other comprehensive loss, beginning of period	(72.0)
Accumulated other comprehensive loss, end of period	(71.3)
After-Tax Amount
Accumulated other comprehensive loss, beginning of period	(230.4)
Amortization of net actuarial losses/prior service cost, after-tax	1.7
Accumulated other comprehensive loss, end of period	(228.7)
Amortization of net actuarial losses
Before-Tax Amount
Amortization of net actuarial losses/prior service cost, before-tax	2.2
Income Tax
Amortization of net actuarial losses/prior service cost, income tax	0.6
After-Tax Amount
Amortization of net actuarial losses/prior service cost, after-tax	1.6
Amortization of prior service cost
Before-Tax Amount
Amortization of net actuarial losses/prior service cost, before-tax	0.2
Income Tax
Amortization of net actuarial losses/prior service cost, income tax	0.1
After-Tax Amount
Amortization of net actuarial losses/prior service cost, after-tax	$ 0.1