Leases - Summary of right-of-use assets and lease liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Jun. 30, 2020
Operating lease assets:
Other assets	$ 44.0	$ 52.0
Operating lease liabilities:
Other accrued liabilities	10.7	11.5
Other liabilities	42.9	50.3
Total operating lease liabilities	$ 53.6	$ 61.8