Investments - Special Deposits (Details) - Deposits with state insurance departments - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	$ 11.7	$ 11.8
New York
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	2.9	2.8
Delaware
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	2.8	2.8
Washington
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	1.2	1.2
Colorado
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	1.1	1.1
Virginia
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.8	0.8
New Mexico
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.7	0.6
New Jersey
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.6	0.6
North Carolina
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.6	0.6
Nevada
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.2	0.4
Florida
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.2	0.2
Massachusetts
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.2	0.2
Kansas
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.2	0.1
Arkansas
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	0.1	0.3
Kentucky
Debt Securities, Available-for-sale [Line Items]
Fixed maturities	$ 0.1	$ 0.1