Pension and Other Postretirement Benefits - Schedule of components of the net periodic benefit cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Pension Plans
Pension and Other Postretirement Benefit Disclosures
Service cost	$ 2.3	$ 2.4	$ 4.6	$ 4.7
Interest cost	13.2	13.0	26.4	26.1
Expected return on plan assets	(16.2)	(16.5)	(32.4)	(33.0)
Amortization of net loss	2.6	3.4	5.2	6.8
Amortization of prior service cost (benefit)	0.5	0.5	1.0	1.0
Net periodic benefit costs	2.4	2.8	4.8	5.6
Other Postretirement Plans
Pension and Other Postretirement Benefit Disclosures
Service cost	0.6	0.7	1.2	1.3
Interest cost	2.5	2.4	5.1	4.8
Expected return on plan assets	(1.7)	(1.7)	(3.5)	(3.5)
Amortization of net loss	0.4	0.7	0.8	1.5
Amortization of prior service cost (benefit)	(1.3)	(1.3)	(2.6)	(2.6)
Net periodic benefit costs	$ 0.5	$ 0.8	$ 1.0	$ 1.5