Debt (Interest Expense) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Debt Disclosure [Abstract]
Cash interest		$ 35.8	$ 31.8	$ 68.2	$ 66.3
Amortization of debt discount and financing costs		3.0	3.0	6.0	7.5
Interest expense, before interest on dissenting shareholders' liability	[1]	38.8	34.8	74.2	73.8
Interest on dissenting shareholders' liability		16.7	13.9	32.6	27.2
Total interest expense		$ 55.5	$ 48.7	$ 106.8	$ 101.0

[1] Represents interest expense before interest on dissenting shareholders' liability.