Pension and Other Postretirement Benefits - Schedule of components of the net periodic benefit cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Settlement charge	$ 8.9	$ 0.0	$ 8.9	$ 0.0
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	2.4	2.4	7.2	7.3
Interest cost	9.8	11.7	29.6	35.1
Expected return on plan assets	(14.1)	(15.5)	(41.9)	(46.6)
Amortization of net loss	3.8	3.9	12.4	11.6
Amortization of prior service cost (benefit)	0.5	0.5	1.5	1.6
Settlement charge	8.9	0.0	8.9	0.0
Net periodic benefit costs	11.3	3.0	17.7	9.0
Other Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.7	0.7	2.0	2.0
Interest cost	1.9	2.3	5.8	6.8
Expected return on plan assets	(1.6)	(1.8)	(4.8)	(5.3)
Amortization of net loss	0.9	0.6	2.7	1.9
Amortization of prior service cost (benefit)	(1.0)	(1.0)	(3.1)	(2.9)
Settlement charge	0.0	0.0	0.0	0.0
Net periodic benefit costs	$ 0.9	$ 0.8	$ 2.6	$ 2.5