Leases - Summary of right-of-use assets and lease liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2021	Jun. 30, 2021
Operating lease assets:
Other assets	$ 32.2	$ 34.3
Operating lease liabilities:
Accrued liabilities	8.8	9.0
Other liabilities	33.4	35.5
Total operating lease liabilities	$ 42.2	$ 44.5