Retirement benefits - Net pension benefit expense (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 20,662	$ 22,810
Interest cost	27,429	25,417
Expected return on plan assets	(67,328)	(66,402)
Amortization of prior service cost	934	843
Amortization of net actuarial loss	37,531	52,331
Amortization of initial net obligation	2	5
Net pension benefit expense	$ 19,230	$ 35,004