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Expected Loss to be Paid (Recovered) - Additional Information (Details) $ in Millions | 3 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Sep. 30, 2024 USD ($) | Sep. 30, 2023 USD ($) | Jun. 30, 2024 | Sep. 30, 2024 USD ($) Curve Payment scenario | Sep. 30, 2023 USD ($) | Dec. 31, 2023 USD ($) scenario
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Period of insured credit performance of guaranteed obligations (in some cases over) |  |  |  | 30 years |  |
Loss and LAE Reserve paid | $ 5 | $ 9 |  | $ 25 | $ 17 |
Expected LAE to be paid | 16 |  |  | 16 |  | $ 22
Credit for estimated future recoveries of claims paid | $ 206 |  |  | $ 206 |  | $ 193
Additional loss recovery assumption, recovery period |  |  |  | 5 years |  |
United States | RMBS | First Lien |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Number of delinquent payments | Payment |  |  |  | 2 |  |
Projected loss assumptions, CDR, plateau rate, projection period |  |  |  | 36 months |  |
Projected loss assumptions, final CPR, period for voluntary prepayments to continue |  |  |  | 12 months |  |
Intermediate conditional default rate (as a percent) | 5.00% |  |  | 5.00% |  |
Number of scenarios weighted in estimating expected losses | scenario |  |  |  | 5 |  | 5
United States | RMBS | First Lien | Base Scenario |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Percent of deferred loan balances to be recovered | 50.00% |  | 30.00% |  |  | 30.00%
Benefit from updated assumptions on expected losses | $ 15 |  |  |  |  |
United States | RMBS | First Lien | Base Scenario |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Projected loss assumptions, CDR, plateau rate, projection period |  |  |  | 36 months |  |
Period from plateau to intermediate conditional default rate (in months) |  |  |  | 12 months |  |
Final conditional default rate as a percentage of plateau conditional default rate |  |  |  | 5.00% |  |
Projected loss assumptions, final CPR, period for voluntary prepayments to continue |  |  |  | 1 year |  |
Default from delinquentor rate, term |  |  |  | 36 months |  |
Performing or projected to reperform, projection period |  |  |  | 36 months |  |
Projected loss assumptions, loss severity, subsequent period |  |  |  | 18 months |  |
Estimated loss severity rate, one through six months (as a percent) |  |  |  | 18 months |  |
Loss severity (as a percent) | 40.00% |  |  | 40.00% |  |
Projected loss assumptions, period to reach final loss severity rate |  |  |  | 2 years 6 months |  |
Final CPR | 15.00% |  |  | 15.00% |  |
United States | RMBS | First Lien | More Stressful Environment |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Period from plateau to intermediate conditional default rate (in months) |  |  |  | 16 months |  |
Projected loss assumptions, period to reach final loss severity rate |  |  |  | 9 years |  |
Percent of deferred loan balances to be recovered |  |  |  | 20.00% |  |
Projected loss assumptions, increase (decrease) in expected loss to be paid, net |  |  |  | $ 33 |  |
United States | RMBS | First Lien | Least Stressful Environment |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Projected loss assumptions, CDR, plateau rate, projection period |  |  |  | 30 months |  |
Period from plateau to intermediate conditional default rate (in months) |  |  |  | 8 months |  |
Percent of deferred loan balances to be recovered |  |  |  | 80.00% |  |
Projected loss assumptions, increase (decrease) in expected loss to be paid, net |  |  |  | $ (31) |  |
Decrease in the plateau period used to calculate potential change in loss estimate (in months) |  |  |  | 6 months |  |
United States | RMBS | Second Lien |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Benefit from updated assumptions on expected losses | $ 29 |  |  |  |  |
Projected loss assumptions, period of consistent conditional default rate |  |  |  | 36 months |  |
Period of conditional default rate downward trend |  |  |  | 1 year |  |
Percent of original period of consistent conditional default rate |  |  |  | 5.00% |  |
Loss recovery assumption (as a percent) | 2.00% |  |  | 2.00% |  | 2.00%
Liquidation rate | 40.00% |  | 50.00% | 40.00% |  |
Number of conditional default rate curves modeled in estimating losses | Curve |  |  |  | 5 |  |
United States | RMBS | Second Lien | More Stressful Environment |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Percent of deferred loan balances to be recovered |  |  |  | 20.00% |  |
United States | RMBS | Second Lien | Least Stressful Environment |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Percent of deferred loan balances to be recovered |  |  |  | 80.00% |  |
United States | RMBS | Second Lien | Home Equity Line of Credit and Closed-end Mortgage |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Final CPR | 15.00% |  |  | 15.00% |  |
United States | RMBS | Second Lien | More Stressful Environment |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Projected loss assumptions, CDR, plateau rate, projection period |  |  |  | 42 months |  |
Period from plateau to intermediate conditional default rate (in months) |  |  |  | 16 months |  |
Increase in conditional default rate ramp down period |  |  |  | 4 months |  |
Stress period (in months) |  |  |  | 58 months |  |
United States | RMBS | Second Lien | More Stressful Environment | Home Equity Line of Credit |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Change in estimate for increased conditional default rate plateau period |  |  |  | $ 81 |  |
United States | RMBS | Second Lien | Least Stressful Environment |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Stress period (in months) |  |  |  | 38 months |  |
Period of constant conditional default rate (in months) |  |  |  | 30 months |  |
Decreased conditional default rate ramp down period |  |  |  | 8 months |  |
Change in estimate for decreased prepayment rate, percent |  |  |  | 10.00% |  |
United States | RMBS | Second Lien | Least Stressful Environment | Home Equity Line of Credit |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Change in estimate for decreased conditional default rate ramp down period |  |  |  | $ 82 |  |
United States | Home Equity Line of Credit |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Initial period for which borrower can pay only interest payments |  |  |  | 10 years |  |
United States | Home Equity Line of Credit Insured |  |  |  |  |  |
Schedule of Expected Losses to be Paid [Line Items] |  |  |  |  |  |
Initial period for which borrower can pay only interest payments |  |  |  | 15 years |  |

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- Definition Represents the initial period over which defaults projected to occur on a pool of insured obligations represent defaults that can be attributed to obligations that are currently delinquent or in foreclosure. + References No definition available. + Details
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