Retirement Benefits - Assumptions used to measure net periodic benefit cost for postretirement plans (Details) - Other Postretirement Benefit Plans, Defined Benefit	12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.15%	3.96%	3.74%
Ultimate medical cost trend rate	4.50%	4.50%	5.00%
Medical cost trend rate decreases to ultimate in year	2025	2025	2021
Discount rate used to measure benefit obligation	3.46%	3.15%
Defined benefit plan, participant age range, Pre-65
Defined Benefit Plan Disclosure [Line Items]
Current medical cost trend rate	7.35%	7.61%	7.75%
Defined benefit plan, participant age range, Post-65
Defined Benefit Plan Disclosure [Line Items]
Current medical cost trend rate	8.68%	9.00%	7.75%