Retirement benefits - Net pension benefit cost recognized (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plans Disclosure
Service cost	$ 20,711	$ 23,632	$ 62,011	$ 70,971
Interest cost	36,027	31,734	107,851	93,202
Expected return on plan assets	(64,437)	(59,480)	(192,963)	(177,277)
Amortization of prior service cost	1,575	1,702	5,190	5,101
Amortization of net actuarial loss	36,278	52,805	110,428	158,557
Amortization of initial net obligation	4	4	14	14
Net pension benefit cost	$ 30,158	$ 50,397	$ 92,531	$ 150,568