Retirement Benefit Obligations - Schedule of Weighted-Average Asset Allocations, by Asset Category (Detail)	Jun. 30, 2020	Jun. 30, 2019
Asset Category:
Benefit plan weighted-average asset allocations	100.00%	100.00%
Equity securities
Asset Category:
Benefit plan weighted-average asset allocations	20.00%	22.00%
Debt securities
Asset Category:
Benefit plan weighted-average asset allocations	68.00%	68.00%
Cash and other
Asset Category:
Benefit plan weighted-average asset allocations	12.00%	10.00%