Income Taxes, Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Deferred tax assets [Abstract]
Accounts receivable	$ 0.2	$ 0.3
Inventories	3.4	4.1
Plant and equipment	1.8	2.3
Pension and employee benefits	32.7	36.0
Net operating and capital losses	73.5	102.5
Credit carryforwards	60.3	36.7
Other, principally accrued liabilities	10.0	9.9
Total gross deferred tax assets	181.9	191.8
Less: valuation allowances	(43.4)	(48.9)
Net deferred tax assets	138.5	142.9
Deferred tax liabilities [Abstract]
Plant and equipment	15.1	17.6
Goodwill	4.8	5.2
Intangible assets	28.8	32.4
Other	0.9	0.7
Total gross deferred tax liabilities	49.6	55.9
Net deferred tax asset	$ 88.9	$ 87.0