Employee Retirement Benefit Plans - Components of Company's Net Periodic Benefit Costs (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Jun. 30, 2019
Components of net periodic benefit cost:
Service cost		$ 0.9	$ 0.9	$ 2.3	$ 2.7
Interest cost		0.7	1.9	4.2	5.7
Expected return on plan assets		(2.5)	(2.7)	(7.8)	(7.9)
Amortization	[1]	2.6	0.6	4.1	1.8
Net amount recognized		1.7	0.7	2.8	2.3
Estimated discounted value of future employer contributions		38.7		38.7		$ 38.8
Estimated annual cash contribution		$ 1.7	$ 1.7	$ 1.7	$ 1.7

[1] Amount represents the amortization of unrecognized actuarial gains/(losses)