Reinsurance - Funds Withheld (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2022 USD ($)	Sep. 30, 2022 USD ($)
Funds Held under Reinsurance Agreements, Asset [Line Items]
Net assets	$ 20,790.8	$ 20,790.8
Funds withheld payable	20,669.7	20,669.7
Embedded derivative asset	4,305.0	4,305.0
Change in fair value of funds withheld embedded derivative	1,237.7	4,305.0
Fixed maturities, available-for-sale
Funds Held under Reinsurance Agreements, Asset [Line Items]
Net assets	16,808.9	16,808.9
Fixed maturities, trading
Funds Held under Reinsurance Agreements, Asset [Line Items]
Net assets	59.4	59.4
Equity securities
Funds Held under Reinsurance Agreements, Asset [Line Items]
Net assets	10.3	10.3
Mortgage loans
Funds Held under Reinsurance Agreements, Asset [Line Items]
Net assets	2,766.2	2,766.2
Other investments
Funds Held under Reinsurance Agreements, Asset [Line Items]
Net assets	32.6	32.6
Cash and cash equivalents
Funds Held under Reinsurance Agreements, Asset [Line Items]
Net assets	989.6	989.6
Accrued interest income
Funds Held under Reinsurance Agreements, Asset [Line Items]
Net assets	182.0	182.0
Net other assets (liabilities)
Funds Held under Reinsurance Agreements, Asset [Line Items]
Net asset (liability)	$ (58.2)	$ (58.2)