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Amount of the collateral pledged in support of federal home loan bank advances outstanding.

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Sum of the carrying amounts as of the balance sheet date of all investments.

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Borrowings and Financing Activities - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Jan. 31, 2024	Jul. 31, 2023	Apr. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Total investments	$ 6,085,654,000				$ 5,693,491,000
Mortgage loans held for sale \| Asset Pledged as Collateral
Debt Instrument [Line Items]
Total investments	31,000,000				2,000,000
Debt Securities \| Fixed-maturities available for sale
Debt Instrument [Line Items]
Investments serving as collateral for FHLB advances	101,000,000				164,000,000
Senior notes
Debt Instrument [Line Items]
Mortgage financing facilities outstanding	$ 1,417,781,000				1,413,504,000
FHLB advances
Debt Instrument [Line Items]
FHLB maturity period	90 days
Federal Home Loan Bank certificates and obligations \| Minimum
Debt Instrument [Line Items]
FHLB ratio of market value to collateral advances	1.03
Federal Home Loan Bank certificates and obligations \| Maximum
Debt Instrument [Line Items]
FHLB ratio of market value to collateral advances	1.14
Mortgages \| Goldman Sachs Master Repurchase Agreement
Debt Instrument [Line Items]
Master repurchase agreements amount			$ 100,000,000		300,000,000
Mortgage financing facilities outstanding	$ 3,000,000
Mortgages \| BMO Master Repurchase Agreement
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				$ 150,000,000	$ 300,000,000
Mortgage financing facilities outstanding	21,000,000
Mortgages \| Flagstar Bank Master Repurchase Agreement \| Subsequent Event
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 150,000,000
Revolving credit facility
Debt Instrument [Line Items]
Line of credit facility, higher borrowing capacity option	400,000,000
Line of credit facility, fair value of amount outstanding	0
Revolving credit facility \| Unsecured revolving credit facility, expiration date 2026
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 275,000,000
Senior Notes Due 2024, 2025 and 2027 \| Senior notes
Debt Instrument [Line Items]
Redemption price, percentage of principal amount	100.00%
Basis spread on variable rate	0.50%
Stock retention percentage required in order to make capital stock transactions	80.00%