Retirement benefits - Net pension benefit cost recognized (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans Disclosure
Service cost	$ 17,983	$ 18,242	$ 38,492	$ 41,300
Interest cost	40,551	36,138	80,417	71,824
Expected return on plan assets	(62,701)	(65,350)	(125,578)	(128,526)
Amortization of prior service cost	1,677	1,511	3,325	3,615
Amortization of net actuarial loss	30,692	35,468	59,985	74,150
Amortization of initial net obligation	4	5	9	10
Net pension benefit cost	$ 28,206	$ 26,014	$ 56,650	$ 62,373