Debt (Interest Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Cash interest	$ 28.3	$ 24.0	$ 94.7	$ 50.4
Amortization of debt discount and financing costs	3.6	3.4	11.0	8.1
Interest expense, before interest on dissenting shareholders' liability	31.9	27.4	105.7	58.5
Interest on dissenting shareholders' liability	14.4	0.0	41.6	0.0
Total interest expense	$ 46.3	$ 27.4	$ 147.3	$ 58.5