CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (PARENTHETICAL) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Other comprehensive (income) loss, pension and other postretirement benefit plans, tax benefit (provision)	$ 2.4	$ 2.2	$ 0.0