Retirement benefits - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Change to spot yield curve approach, effect on pension expense	$ 8,000		$ 25,000
Other Postretirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net pension benefit cost	1,034	$ 1,001	3,266	$ 7,696
Special termination cost				4,521
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net pension benefit cost	50,397	57,845	150,568	181,985
Special termination cost	$ 0	$ 0	$ 0	$ 7,088