Retirement Benefits - Assumptions used to measure net periodic benefit cost for postretirement plans (Details) - Other Postretirement Benefits Plan	12 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2021
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.26%	2.36%	2.14%
Ultimate medical cost trend rate	4.50%	4.50%	4.50%
Medical cost trend rate decreases to ultimate in year	2031	2029	2028
Defined benefit plan, participant age range, Pre-65
Defined Benefit Plan Disclosure [Line Items]
Current medical cost trend rate	6.73%	6.45%	6.73%
Defined benefit plan, participant age range, Post-65
Defined Benefit Plan Disclosure [Line Items]
Current medical cost trend rate	6.81%	6.72%	7.03%