CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Statement of Comprehensive Income [Abstract]
Net income	$ 1,906.9	$ 2,237.7	$ 1,285.5
Components of other comprehensive income:
Actuarial gains related to defined benefit pension plans, net of tax effect	0.6	16.6	7.8
Change in net foreign currency translation adjustment	0.0	(0.1)	(2.2)
Other comprehensive income, net of tax effect	0.6	16.5	5.6
Comprehensive income	$ 1,907.5	$ 2,254.2	$ 1,291.1