Investments - Mortgage Loans, Residential by State (Details) - Geographic Concentration Risk - Residential mortgage loans - Mortgage Loans, Net	Mar. 31, 2021	Dec. 31, 2020
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	100.00%	100.00%
California
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	23.30%	24.80%
Florida
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	12.60%	13.30%
NEW YORK
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	6.70%	6.20%
Other U.S. States
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	43.10%	41.10%
Total U.S. Region
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	85.70%	85.40%
IRELAND
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	11.10%	12.90%
Other
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	3.20%	1.70%
International
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	14.30%	14.60%