Accrued Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Jun. 30, 2018
Accrued Liabilities, Current [Abstract]
Accrued compensation and benefits	$ 51.1	$ 83.3
Accrued postretirement benefits	15.4	15.4
Deferred revenue	14.2	10.4
Derivative financial instruments	12.7	0.0
Accrued interest expense	10.4	10.4
Accrued pension liabilities	3.3	3.3
Accrued income taxes	1.9	1.4
Other	22.3	24.4
Total accrued liabilities	$ 131.3	$ 148.6