Retirement Benefit Obligations - Schedule of Weighted-Average Asset Allocations, by Asset Category (Detail)	Jun. 30, 2018	Jun. 30, 2017
Asset Category:
Benefit plan weighted-average asset allocations	100.00%	100.00%
Equity Securities [Member]
Asset Category:
Benefit plan weighted-average asset allocations	23.00%	22.00%
Debt Securities [Member]
Asset Category:
Benefit plan weighted-average asset allocations	65.00%	62.00%
Cash and Other [Member]
Asset Category:
Benefit plan weighted-average asset allocations	12.00%	16.00%