Retirement benefits - Net pension benefit expense (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 21,016	$ 20,967	$ 63,215	$ 61,965
Interest cost	25,661	36,389	76,833	106,233
Expected return on plan assets	(67,201)	(68,058)	(200,410)	(198,836)
Amortization of prior service cost	1,294	1,411	3,583	4,229
Amortization of net actuarial loss	51,094	41,200	156,254	123,540
Amortization of initial net obligation	4	4	13	13
Net pension benefit expense	$ 31,868	$ 31,913	$ 99,488	$ 97,144