Retirement benefits - Net pension benefit cost (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plans Disclosure
Service cost	$ 19,126	$ 20,711	$ 57,618	$ 62,011
Interest cost	40,124	36,027	120,541	107,851
Expected return on plan assets	(62,844)	(64,437)	(188,422)	(192,963)
Amortization of prior service cost	1,665	1,575	4,990	5,190
Amortization of net actuarial loss	29,988	36,278	89,973	110,428
Amortization of initial net obligation	4	4	13	14
Net pension benefit cost	$ 28,063	$ 30,158	$ 84,713	$ 92,531