Investments - Mortgage Loans, Residential by State (Details) - Geographic Concentration Risk - Residential mortgage loans - Mortgage Loans, Net	Dec. 31, 2021	Mar. 31, 2021
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	28.40%	31.60%
Florida
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	11.40%	10.00%
NEW YORK
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	5.10%	5.10%
Other U.S. States
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	43.30%	39.80%
Total U.S. Region
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	88.20%	86.50%
IRELAND
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	6.40%	4.10%
UNITED KINGDOM
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	3.80%	5.10%
Other
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	1.60%	4.30%
International
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	11.80%	13.50%