Retirement benefits - Net pension benefit expense (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 14,599	$ 18,238	$ 42,534	$ 57,599
Interest cost	59,021	27,953	166,456	82,941
Expected return on plan assets	(80,137)	(67,024)	(228,695)	(201,487)
Amortization of prior service cost	227	1,028	679	3,084
Amortization of net actuarial (gain) loss	(657)	39,570	12,625	118,186
Amortization of initial net obligation	0	2	0	6
Net pension benefit expense	$ (6,947)	$ 19,767	$ (6,401)	$ 60,329