Retirement benefits - Net pension benefit expense (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 18,238	$ 21,016	$ 57,599	$ 63,215
Interest cost	27,953	25,661	82,941	76,833
Expected return on plan assets	(67,024)	(67,201)	(201,487)	(200,410)
Amortization of prior service cost	1,028	1,294	3,084	3,583
Amortization of net actuarial loss	39,570	51,094	118,186	156,254
Amortization of initial net obligation	2	4	6	13
Net pension benefit expense	$ 19,767	$ 31,868	$ 60,329	$ 99,488