Income Taxes, Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Mar. 31, 2017
Deferred tax assets [Abstract]
Accounts receivable	$ 0.3	$ 0.4
Inventories	4.1	5.0
Plant and equipment	2.3	3.7
Pension and employee benefits	36.0	51.8
Net operating loss, capital loss and credit carryforwards	139.2	147.5
Other, principally accrued liabilities	9.9	10.9
Total gross deferred tax assets	191.8	219.3
Less: valuation allowances	(48.9)	(49.6)
Net deferred tax assets	142.9	169.7
Deferred tax liabilities [Abstract]
Plant and equipment	17.6	21.2
Goodwill	5.2	4.7
Intangible assets	32.4	43.3
Other	0.7	1.8
Total gross deferred tax liabilities	55.9	71.0
Net deferred tax asset	$ 87.0	$ 98.7