Investment Securities - Investments In Private Equity Funds Subject to Lock-Up Periods (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Investment securities
Investments held in trusts	$ 500.5	$ 479.5
Lloyds Bank
Investment securities
Fair value investments	319.2	342.8
Investments held in trusts	137.4	$ 113.8
Bank loan fund
Investment securities
Fair value investments	174.8
ILS funds
Investment securities
Fair value investments	49.3
Commitments to funds	100.0
Insurance-Linked Securities Funds Receivable
Investment securities
Fair value investments	70.0
Private equity funds
Investment securities
Trading security, fair value	140.6
1 – 3 years | Private equity funds
Investment securities
Trading security, fair value	4.2
3 – 5 years | Private equity funds
Investment securities
Trading security, fair value	18.8
5 – 10 years | Private equity funds
Investment securities
Trading security, fair value	113.9
>10 years | Private equity funds
Investment securities
Trading security, fair value	$ 3.7