Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Statement of Stockholders' Equity [Abstract]
Unrealized gain (loss) on interest rate derivatives, income tax expense (benefit)	$ (1.2)	$ (3.9)	$ (4.3)
Change in pension and other postretirement defined benefit plans - income tax (expense) benefit	$ (2.8)	$ (2.3)	$ (4.4)