Debt - Summary of Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 662.8	$ 1,146.7
Federal Home Loan Bank Advances (FHLB)
Debt Instrument [Line Items]
Long-term debt, carrying value	0.0	$ 155.0
FHLBC fixed interest rate		1.91%
Senior Notes | 5.75% Senior Notes due 2023
Debt Instrument [Line Items]
Long-term debt, carrying value	0.0	$ 241.3
Senior Notes | 5.25% Senior Notes due 2028
Debt Instrument [Line Items]
Long-term debt, carrying value	641.7	640.2
Convertible Junior Subordinated Debentures, at 9% per annum, Due 2063
Debt Instrument [Line Items]
Long-term debt, carrying value	$ 21.1	$ 110.2