Retirement benefits - Net pension benefit cost (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plans Disclosure
Service cost	$ 19,549	$ 20,509
Interest cost	33,993	39,866
Expected return on plan assets	(63,895)	(62,877)
Amortization of prior service cost	1,509	1,648
Amortization of net actuarial loss	39,561	29,293
Amortization of initial net obligation	4	4
Net pension benefit expense	$ 30,721	$ 28,443