Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Accrued postretirement benefits cost	$ 12.4	$ 15.4
Accrued pension cost	49.9	57.4
Other employee benefit accruals	15.7	11.0
Tax loss and credit carryforwards	83.2	90.2
Other, net	63.9	46.7
Valuation allowances	(31.0)	(36.7)
Total deferred tax assets	194.1	184.0
Deferred tax liabilities - principally depreciation and amortization	(247.9)	(255.7)
Net deferred tax liabilities	$ (53.8)	$ (71.7)