Significant Accounting Policies - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 1,212.8	$ 1,070.6	$ 588.0
Other comprehensive (loss) income, net of tax	(22.5)	62.9	2.0
Ending balance	1,231.0	1,212.8	1,070.6
Interest Rate Derivatives
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(3.7)	(9.5)	(16.9)
Other comprehensive (loss) income before reclassifications	0.0	0.0	1.1
Amounts reclassified from accumulated other comprehensive income (loss)	4.5	5.8	6.3
Other comprehensive (loss) income, net of tax	4.5	5.8	7.4
Ending balance	0.8	(3.7)	(9.5)
Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(42.2)	(99.3)	(86.5)
Other comprehensive (loss) income before reclassifications	(39.4)	57.1	(12.8)
Amounts reclassified from accumulated other comprehensive income (loss)	21.5	0.0	0.0
Other comprehensive (loss) income, net of tax	(17.9)	57.1	(12.8)
Ending balance	(60.1)	(42.2)	(99.3)
Pension and Postretirement Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(28.2)	(28.2)	(35.6)
Other comprehensive (loss) income before reclassifications	(8.5)	1.4	9.2
Amounts reclassified from accumulated other comprehensive income (loss)	(0.6)	(1.4)	(1.8)
Other comprehensive (loss) income, net of tax	(9.1)	0.0	7.4
Ending balance	(37.3)	(28.2)	(28.2)
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(74.1)	(137.0)	(139.0)
Other comprehensive (loss) income before reclassifications	(47.9)	58.5	(2.5)
Amounts reclassified from accumulated other comprehensive income (loss)	25.4	4.4	4.5
Other comprehensive (loss) income, net of tax	(22.5)	62.9	2.0
Ending balance	$ (96.6)	$ (74.1)	$ (137.0)