v3.25.2
Expected Loss to be Paid (Recovered) - Additional Information (Details)
€ in Millions, $ in Millions, £ in Billions
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 26, 2023
USD ($)
Jun. 30, 2025
USD ($)
Jun. 30, 2024
USD ($)
Jun. 30, 2025
USD ($)
Payment
Jun. 30, 2024
USD ($)
Dec. 31, 2024
USD ($)
Jun. 30, 2025
GBP (£)
Jun. 30, 2025
EUR (€)
Mar. 31, 2025
USD ($)
Mar. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
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 $ 13 $ (56) $ 20            
Expected LAE to be paid   8   8   $ 11          
Credit for estimated future recoveries of claims paid   258   258   262          
Net   272,778   272,778   261,552          
Insured financial obligations insured contractual payments outstanding, net   434,562   $ 434,562   415,966          
Additional loss recovery assumption, recovery period       5 years              
Net Expected Loss to be Paid (Recovered)   186 447 $ 186 447 106     $ 150 $ 433 $ 505
BIG                      
Schedule of Expected Losses to be Paid [Line Items]                      
Net   10,508   10,508   10,182          
Puerto Rico Electric Power Authority | Guarantee Obligations                      
Schedule of Expected Losses to be Paid [Line Items]                      
Damages sought, estimate $ 2,400                    
Damages sought $ 8,500                    
UK Regulated Utilities | BIG                      
Schedule of Expected Losses to be Paid [Line Items]                      
Net   5,300   5,300     £ 3.8        
European Renewable Energy | BIG                      
Schedule of Expected Losses to be Paid [Line Items]                      
Net   934   934       € 792      
Thames Water Utilities Finance PLC | BIG                      
Schedule of Expected Losses to be Paid [Line Items]                      
Net   2,400   2,400              
United States | RMBS                      
Schedule of Expected Losses to be Paid [Line Items]                      
Net   1,436   1,436   1,507          
Net Expected Loss to be Paid (Recovered)   (35) $ 0 (35) $ 0 (43)     $ (37) $ (2) $ 43
United States | RMBS | BIG                      
Schedule of Expected Losses to be Paid [Line Items]                      
Net   $ 791   $ 791   $ 819          
United States | RMBS | First Lien                      
Schedule of Expected Losses to be Paid [Line Items]                      
Projected loss assumptions, CDR, plateau rate, projection period       36 months              
Number of delinquent payments | Payment       2              
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%       50.00%          
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              
Projected loss assumptions, final CPR, period for voluntary prepayments to continue       1 year              
Estimated loss severity rate, one through six months (as a percent)       18 months              
Loss severity (as a percent)   40.00%   40.00%     40.00% 40.00%      
Projected loss assumptions, period to reach final loss severity rate       2 years 6 months              
United States | RMBS | First Lien | More Stressful Environment                      
Schedule of Expected Losses to be Paid [Line Items]                      
Projected loss assumptions, period to reach final loss severity rate       9 years              
Percent of deferred loan balances to be recovered       20.00%              
Period from plateau to intermediate conditional default rate (in months)       16 months              
Projected loss assumptions, increase (decrease) in expected loss to be paid, net       $ 32              
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              
Percent of deferred loan balances to be recovered       80.00%              
Period from plateau to intermediate conditional default rate (in months)       8 months              
Decrease in the plateau period used to calculate potential change in loss estimate (in months)       6 months              
Projected loss assumptions, increase (decrease) in expected loss to be paid, net       $ (30)              
United States | RMBS | Second Lien                      
Schedule of Expected Losses to be Paid [Line Items]                      
Loss recovery assumption (as a percent)   2.00%   2.00%   2.00% 2.00% 2.00%      
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%              
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 | 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       $ 75              
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       $ 75              
Puerto Rico                      
Schedule of Expected Losses to be Paid [Line Items]                      
Net   $ 637   637   $ 637          
Insured financial obligations insured contractual payments outstanding, net   742   742   756          
Puerto Rico | Other Puerto Rico Exposure                      
Schedule of Expected Losses to be Paid [Line Items]                      
Net   92   92   92          
Puerto Rico | Puerto Rico Defaulted Exposures Subject to a Plan Support Agreement | Puerto Rico Electric Power Authority                      
Schedule of Expected Losses to be Paid [Line Items]                      
Net   532   532   532          
Insured financial obligations insured contractual payments outstanding, net   $ 617   $ 617   $ 629