CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 349.4	$ 570.6	$ 355.9
Available-for-sale securities:
Unrealized holding losses, net of tax effect	0.0	0.0	(5.6)
Reclassification of realized transactions, net of tax effect	0.0	0.0	5.6
Defined benefit plans:
Actuarial (losses) gains related to defined benefit pension plans, net of tax effect	(9.4)	1.4	2.9
Reclassification of realized transactions, net of tax effect	1.1	0.8	1.0
Change in net foreign currency translation adjustment	3.7	(1.8)	(5.3)
Other comprehensive (loss) income, net of tax effect	(4.6)	0.4	(1.4)
Comprehensive income	$ 344.8	$ 571.0	$ 354.5