Supplemental Financial Information (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Supplemental Cash Flow Information [Abstract]
Cash paid for income taxes	$ 25.9	$ 48.4	$ 25.4
Cash paid for interest on borrowings	85.3	82.5	52.9
Allowance for Doubtful Accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balances at Beginning of Year	2.1	2.5	2.6
Charged to Cost and Expense	0.2	0.2	0.1
Deductions	(0.1)	(0.6)	(0.2)
Balance at End of Year	2.2	2.1	2.5
Valuation Allowance of Deferred Tax Assets
Movement in Valuation Allowances and Reserves [Roll Forward]
Balances at Beginning of Year	210.1	161.8	116.5
Charged to Cost and Expense	36.2	15.2	5.5
Charged to Other Accounts	0.0	37.6	47.8
Deductions	(41.8)	(4.5)	(8.0)
Balance at End of Year	$ 204.5	$ 210.1	$ 161.8