Fair Value Measurements - Schedule of investments measured at NAV (Details) - USD ($) $ in Millions		Sep. 30, 2021	Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unfunded commitments		$ 51.8	$ 9.5
Nonredeemable Investments with known liquidation periods
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment	[1]	53.9	51.2
Nonredeemable Investments With Unknown Liquidation Periods
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment	[1]	46.6	42.6
Redeemable Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Alternative Investment	[2]	$ 26.9	$ 27.3

[1] The investments are expected to be returned through distributions over the life of the funds as a result of liquidations of the funds’ underlying assets. Investments with known liquidation periods have an expected weighted-average life of 4.0 years and 1.9 years at September 30, 2021 and 2020.

[2] Investments are redeemable on a monthly and quarterly basis.