Pension and Postretirement Benefit Plans (Net Periodic Pension Costs Included in Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
After-Tax Amount
Net losses reclassified from accumulated other comprehensive loss into income	$ 3.4	$ 3.6
Defined Benefit Pension Plans
Before-Tax Amount
Accumulated other comprehensive loss, beginning of period	(393.2)
Net gains reclassified from accumulated other comprehensive loss into income	4.0	3.5
Accumulated other comprehensive, end of period	(389.2)
Income Tax
Accumulated other comprehensive loss, beginning of period	(96.8)
Amortization of prior service cost and net actual loss	0.5	0.5
Accumulated other comprehensive loss, end of period	(96.3)
After-Tax Amount
Accumulated other comprehensive loss, beginning of period	(296.4)
Net losses reclassified from accumulated other comprehensive loss into income	3.5	3.0
Accumulated other comprehensive loss, end of period	(292.9)
Amortization of net actuarial losses
Before-Tax Amount
Net gains reclassified from accumulated other comprehensive loss into income	3.5	3.1
Income Tax
Amortization of prior service cost and net actual loss	0.5
After-Tax Amount
Net losses reclassified from accumulated other comprehensive loss into income	3.0
Amortization of prior service cost
Before-Tax Amount
Net gains reclassified from accumulated other comprehensive loss into income	0.5	$ 0.4
Income Tax
Amortization of prior service cost and net actual loss	0.0
After-Tax Amount
Net losses reclassified from accumulated other comprehensive loss into income	$ 0.5