Retirement benefits - Net pension benefit expense (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 14,253	$ 20,662
Interest cost	46,351	27,429
Expected return on plan assets	(66,345)	(67,328)
Amortization of prior service cost	210	934
Amortization of net actuarial loss	6,443	37,531
Amortization of initial net obligation	0	2
Net pension benefit expense	$ 912	$ 19,230