Income Taxes - Effective Income Tax Rate Reconciliation (Parenthetical) (Detail) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2017
Income Taxes Disclosure [Line Items]
U.S. federal income tax rate	[1]		21.00%	28.00%	35.00%
Non-cash impairment charge			$ 96.0	$ 280.0	$ 785.0
Non-cash impairment charge		$ 41.0	49.0	218.0	48.0
Income tax expense, net			$ 126.0	355.0	28.0
Foreign tax authority settlement, net income tax expense (benefit)				$ 49.0	$ 63.0
Effective tax rate	[2]		36.00%	(33.00%)	(5.00%)
United Kingdom Fixed Assets [Member]
Income Taxes Disclosure [Line Items]
Non-cash impairment charge					$ 360.0
Non-deductible goodwill, asset and investment impairment					29.0
Australian Subsidiaries [Member]
Income Taxes Disclosure [Line Items]
Non-cash impairment charge				$ 1.1
Non-cash impairment charge			$ 96.0	218.0
Current Income Tax Expense [Member]
Income Taxes Disclosure [Line Items]
Foreign tax authority settlement, net income tax expense (benefit)				2.0
Deferred Income Taxes [Member]
Income Taxes Disclosure [Line Items]
Foreign tax authority settlement, net income tax expense (benefit)				47.0
U.S. Tax Cuts and Jobs Act [Member]
Income Taxes Disclosure [Line Items]
Income tax expense, net			237.0	237.0
Foreign Tax Authority [Member] | SEC Schedule, 12-09, Valuation Allowance, Operating Loss Carryforward [Member]
Income Taxes Disclosure [Line Items]
Change in valuation allowance tax benefit					40.0
Goodwill [Member]
Income Taxes Disclosure [Line Items]
Non-deductible goodwill, asset and investment impairment					$ 12.0
Goodwill [Member] | Australian Subsidiaries [Member]
Income Taxes Disclosure [Line Items]
Non-deductible goodwill, asset and investment impairment			$ 10.0	54.0
Asset And Investment [Member] | Australian Subsidiaries [Member]
Income Taxes Disclosure [Line Items]
Non-deductible goodwill, asset and investment impairment				$ 301.0

[1] As the Company has a June 30 fiscal year-end, the impact of the lower tax rate from the Tax Act was phased in resulting in a U.S. statutory federal tax rate of approximately 28% for the fiscal year ended June 30, 2018 and a 21% U.S. statutory federal tax rate for fiscal years thereafter.

[2] For the fiscal year ended June 30, 2019, the effective tax rate of 36% represents income tax expense when compared to consolidated pre-tax book income. For the fiscal years ended June 30, 2018 and 2017, the effective tax rates of (33)% and (5)%, respectively, represent income tax expense when compared to consolidated pre-tax book loss.