Retirement benefits - Net pension benefit cost recognized (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plans Disclosure
Service cost	$ 23,058	$ 24,223
Interest cost	35,686	31,496
Expected return on plan assets	(63,176)	(57,617)
Amortization of prior service cost	2,104	1,716
Amortization of net actuarial loss	38,682	51,427
Amortization of initial net obligation	5	5
Net pension benefit cost	$ 36,359	$ 51,250