Retirement benefits - Net pension benefit cost recognized (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plans Disclosure
Service cost	$ 20,509	$ 23,058
Interest cost	39,866	35,686
Expected return on plan assets	(62,877)	(63,176)
Amortization of prior service cost	1,648	2,104
Amortization of net actuarial loss	29,293	38,682
Amortization of initial net obligation	4	5
Net pension benefit cost	$ 28,443	$ 36,359