Retirement benefits - Net pension benefit expense (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 18,699	$ 19,389	$ 39,361	$ 42,199
Interest cost	27,559	25,755	54,988	51,172
Expected return on plan assets	(67,135)	(66,807)	(134,463)	(133,209)
Amortization of prior service cost	1,122	1,446	2,056	2,289
Amortization of net actuarial loss	41,085	52,829	78,616	105,160
Amortization of initial net obligation	2	4	4	9
Net pension benefit expense	$ 21,332	$ 32,616	$ 40,562	$ 67,620