Retirement benefits - Net pension benefit expense (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 13,682	$ 18,699	$ 27,935	$ 39,361
Interest cost	61,084	27,559	107,435	54,988
Expected return on plan assets	(82,213)	(67,135)	(148,558)	(134,463)
Amortization of prior service cost	242	1,122	452	2,056
Amortization of net actuarial loss	6,839	41,085	13,282	78,616
Amortization of initial net obligation	0	2	0	4
Net pension benefit expense	$ (366)	$ 21,332	$ 546	$ 40,562