Leases - Summary of right-of-use assets and lease liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Jun. 30, 2020
Operating lease assets:
Other assets	$ 46.6	$ 52.0
Operating lease liabilities:
Other accrued liabilities	11.1	11.5
Other liabilities	45.3	50.3
Total operating lease liabilities	$ 56.4	$ 61.8