Pension and Other Postretirement Benefits - Schedule of components of the net periodic benefit cost (Details) - Three Months Ended September 30, - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Pension and Other Postretirement Benefit Disclosures
Service cost	$ 2.4	$ 2.3
Interest cost	11.7	13.2
Expected return on plan assets	(15.5)	(16.2)
Amortization of net loss	3.9	2.6
Amortization of prior service cost (benefit)	0.5	0.5
Net periodic benefit costs	3.0	2.4
Service cost	0.7	0.6
Interest cost	2.3	2.5
Expected return on plan assets	(1.8)	(1.7)
Amortization of net loss	0.6	0.4
Amortization of prior service cost (benefit)	(1.0)	(1.3)
Net periodic benefit costs	$ 0.8	$ 0.5