Supplemental Balance Sheet Information - Prepaid and Other Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Jun. 30, 2017
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid Expense, Current	$ 23.7	$ 12.3
Spare parts supplies	11.9	11.8
Prepaid Taxes	12.1	11.5
Short term deferred financing costs	6.1	0.0
Value Added Tax Receivable	23.4	16.0
Available-for-sale Securities, Current	13.4	18.6
Other current assets	33.6	27.6
Prepaid expenses and other	$ 124.2	$ 97.8