Derivative Instruments and Hedging Activities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2018
Derivative [Line Items]
Total long-term debt	$ 2,199.9		$ 2,199.9		$ 2,721.3
Unrealized foreign exchange gain/(loss) within other comprehensive income	15.6	$ (3.9)	11.4	$ (21.5)
Unrealized foreign exchange gain/(loss) within statement of operations	9.4	$ (2.8)	6.9	$ (16.2)
Net accumulated gain related to investment hedges			59.0
Euro Denominated Debt Outstanding [Member]
Derivative [Line Items]
Total long-term debt	$ 777.7		$ 777.7