Retirement benefits - Net pension (benefit) expense (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2024	Dec. 31, 2023
U.S. Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 6,973	$ 6,747	$ 13,946	$ 14,651
Interest cost	46,013	47,726	92,026	94,752
Expected return on plan assets	(61,244)	(64,383)	(122,487)	(128,765)
Amortization of prior service cost	762	243	1,525	454
Amortization of net actuarial loss	2,578	1,207	5,155	803
Net pension (benefit) expense	(4,918)	(8,460)	(9,835)	(18,105)
Non-U.S. Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	5,440	5,673	11,081	11,296
Interest cost	18,604	19,826	37,806	39,681
Expected return on plan assets	(21,250)	(23,850)	(43,179)	(47,716)
Amortization of prior service cost	64	91	128	182
Amortization of net actuarial loss	1,614	1,586	3,286	3,172
Net pension (benefit) expense	$ 4,472	$ 3,326	$ 9,122	$ 6,615