Assumptions Used to Measure Net Periodic Benefit Cost for Postretirement Plans (Detail) - Other Postretirement Benefit Plans, Defined Benefit	12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2014
Schedule of Net Periodic Benefit Costs Weighted Average Assumptions [Line Items]
Discount rate used to measure net periodic benefit cost	3.96%	3.74%	4.10%
Ultimate medical cost trend rate	4.50%	5.00%	5.00%
Medical cost trend rate decreases to ultimate in year	2025	2021	2021
Defined benefit plan, participant age range, Pre-65 [Member]
Schedule of Net Periodic Benefit Costs Weighted Average Assumptions [Line Items]
Current medical cost trend rate	7.61%	7.75%	7.75%
Defined benefit plan, participant age range, Post-65 [Member] [Member]
Schedule of Net Periodic Benefit Costs Weighted Average Assumptions [Line Items]
Current medical cost trend rate	9.00%	7.75%	7.75%