Postretirement and Other Employee Benefits - Summary of Weighted-Average Assumptions Used to Determine Net Benefit Costs and Benefit Obligations (Detail)	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Weighted-average assumptions used to determine net benefit costs:
Discount rate	0.40%	0.90%	0.70%
Expected return on plan assets	3.25%	3.75%	3.50%
Rate of compensation increase	1.75%	1.75%	1.50%
Weighted-average assumptions used to determine benefit obligations at year end:
Discount rate	0.25%	0.40%	0.90%
Expected return on plan assets	2.75%	3.25%	3.75%
Rate of compensation increase	1.50%	1.75%	1.75%