Significant Accounting Policies, New Accounting Guidance (Details) - USD ($) $ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
New Accounting Guidance [Abstract]
Net periodic benefit cost	[1]	$ 3.3	$ 2.9	$ 44.6
Retained earnings		394.9	372.4
Deferred income taxes		96.9	108.4
Equity		490.1	414.0
Cost of Sales [Member]
New Accounting Guidance [Abstract]
Net periodic benefit cost			(1.1)	(10.1)
SG&A [Member]
New Accounting Guidance [Abstract]
Net periodic benefit cost			(1.8)	(34.5)
Other Income Expense [Member]
New Accounting Guidance [Abstract]
Net periodic benefit cost			$ 2.9	$ 44.6
ASU 2016-16 [Member]
New Accounting Guidance [Abstract]
Retained earnings		(8.0)
ASU 2016-09 [Member]
New Accounting Guidance [Abstract]
Deferred income taxes		0.4
Equity		$ 0.4

[1] Represents net periodic benefit cost, exclusive of service cost, for the Company's pension and postretirement plans.