Investments - Schedule of Commercial Mortgage Loans (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at cost	$ 234.9	$ 144.8
Total Loans Member
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at cost	435.6	144.8
Mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at cost	234.9	144.8
Private loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at cost	200.7	0.0
Fair Value | Total Loans Member
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at cost	442.1	148.8
Fair Value | Mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at cost	240.3	148.8
Fair Value | Private loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, at cost	$ 201.8	$ 0.0