Income Taxes, Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Mar. 31, 2019
Deferred tax assets [Abstract]
Accounts receivable	$ 0.3	$ 0.2
Inventories	4.5	3.4
Plant and equipment	4.7	1.8
Lease liabilities	15.7	0.0
Pension and employee benefits	45.1	32.7
Net operating and capital losses	70.2	73.5
Credit carryforwards	56.8	60.3
Other, principally accrued liabilities	8.1	10.0
Total gross deferred tax assets	205.4	181.9
Less: valuation allowances	(46.9)	(43.4)
Net deferred tax assets	158.5	138.5
Deferred tax liabilities [Abstract]
Plant and equipment	13.1	15.1
Lease assets	15.6	0.0
Goodwill	4.8	4.8
Intangible assets	26.4	28.8
Other	1.9	0.9
Total gross deferred tax liabilities	61.8	49.6
Net deferred tax asset	$ 96.7	$ 88.9