Retirement benefits - Net pension (benefit) expense (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
U.S. Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 6,973	$ 7,904
Interest cost	46,013	47,026
Expected return on plan assets	(61,243)	(64,382)
Amortization of prior service cost	763	211
Amortization of net actuarial loss (gain)	2,577	(404)
Net pension (benefit) expense	(4,917)	(9,645)
Non-U.S. Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	5,641	5,623
Interest cost	19,202	19,855
Expected return on plan assets	(21,929)	(23,866)
Amortization of prior service cost	64	91
Amortization of net actuarial loss (gain)	1,672	1,586
Net pension (benefit) expense	$ 4,650	$ 3,289