Investments - Summary of Investments (Details) - USD ($) $ in Millions	Jun. 30, 2023	Sep. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Fixed income securities	$ 0.6	$ 12.6
Equity securities	863.9	928.8
Equity securities (other)	81.4	76.4
Other	56.7	50.8
Total investments	1,002.6	1,068.6
Less: Short-term Investments	(0.6)	(12.6)
Long-term investments	$ 1,002.0	$ 1,056.0