Retirement Benefits - Assumptions used to measure net periodic benefit cost for postretirement plans (Details) - Other Postretirement Benefits Plan	12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2022
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.86%	4.26%	2.36%
Ultimate medical cost trend rate	4.50%	4.50%	4.50%
Medical cost trend rate decreases to ultimate in year	2033	2031	2029
Defined benefit plan, participant age range, Pre-65
Defined Benefit Plan Disclosure [Line Items]
Current medical cost trend rate	7.85%	6.73%	6.45%
Defined benefit plan, participant age range, Post-65
Defined Benefit Plan Disclosure [Line Items]
Current medical cost trend rate	8.18%	6.81%	6.72%