Freestanding Derivative Forward Contracts (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Percentage Of Company Sales Denominated In Us Dollars	99.00%
Foreign currency transaction gains (loss), before tax	$ 9.3	$ 1.0	$ 0.7
Foreign Exchange Forward
Derivative [Line Items]
Gain (loss) on foreign currency derivatives	$ 4.2	$ (2.3)