Income Taxes, Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020
Deferred tax assets [Abstract]
Accounts receivable	$ 0.3	$ 0.3
Inventories	4.5	4.5
Plant and equipment	7.5	4.7
Lease liabilities	14.0	15.7
Pension and employee benefits	24.0	45.1
Net operating and capital losses	52.7	70.2
Credit carryforwards	51.8	56.8
Other, principally accrued liabilities	8.9	8.1
Total gross deferred tax assets	163.7	205.4
Less: valuation allowances	(90.7)	(46.9)
Net deferred tax assets	73.0	158.5
Deferred tax liabilities [Abstract]
Plant and equipment	9.8	13.1
Lease assets	13.8	15.6
Goodwill	5.1	4.8
Intangible assets	25.1	26.4
Other	0.6	1.9
Total gross deferred tax liabilities	54.4	61.8
Net deferred tax asset	$ 18.6	$ 96.7