v3.26.3
Expected Loss to be Paid (Recovered) - Additional Information (Details)
€ in Millions, £ in Millions, $ in Millions
 1 Months Ended 3 Months Ended 9 Months Ended
Sep. 18, 2025
board_member
Aug. 31, 2025
board_member
Sep. 30, 2026
USD ($)
Sep. 30, 2025
USD ($)
Sep. 30, 2026
USD ($)
Payment
Sep. 30, 2025
USD ($)
Sep. 30, 2026
GBP (£)
Sep. 30, 2026
EUR (€)
Sep. 24, 2026
USD ($)
Dec. 31, 2025
USD ($)
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     $ 4 $ 5 $ 8 $ (51)        
Expected LAE to be paid     7   7         $ 8
Credit for estimated future recoveries of claims paid     321   321         311
Net     281,100   281,100         277,100
Insured financial obligations insured contractual payments outstanding, net     449,700   449,700         440,800
Plaintiff, terminated board members | board_member   6                
Plaintiff, total board members | board_member   7                
Plaintiff, terminated board members suing for reinstatement | board_member 3                  
Brightline Trains Florida LLC                    
Schedule of Expected Losses to be Paid [Line Items]                    
Proceeds from affiliates exit from Chapter 11, estimated                 $ 490  
Proceeds from affiliates exit from Chapter 11, post-petition funding                 258  
Brightline Trains Florida LLC | Junior Subordinated Debt                    
Schedule of Expected Losses to be Paid [Line Items]                    
Debt instrument, face amount                 350  
Brightline Trains Florida LLC | Senior Subordinated Notes                    
Schedule of Expected Losses to be Paid [Line Items]                    
Debt instrument, face amount                 140  
BIG                    
Schedule of Expected Losses to be Paid [Line Items]                    
Net     8,020   8,020         8,760
Brightline Trains Florida LLC                    
Schedule of Expected Losses to be Paid [Line Items]                    
Insured financial obligations, loan payments                 70  
Brightline Trains Florida LLC | Senior Subordinated Notes                    
Schedule of Expected Losses to be Paid [Line Items]                    
Insured financial obligations, loan payments                 $ 122  
Thames Water Utilities Finance PLC | BIG                    
Schedule of Expected Losses to be Paid [Line Items]                    
Net     2,400   2,400   £ 1,800      
U.S. Transportation | BIG                    
Schedule of Expected Losses to be Paid [Line Items]                    
Net     $ 1,100   $ 1,100          
Insured financial obligations, net, percent     0.51   0.51   0.51 0.51    
European Renewable Energy | BIG                    
Schedule of Expected Losses to be Paid [Line Items]                    
Net     $ 571   $ 571     € 504    
U.K. Student Accommodations | BIG                    
Schedule of Expected Losses to be Paid [Line Items]                    
Net     385   385   £ 290      
U.K. National Health Service Trusts | BIG                    
Schedule of Expected Losses to be Paid [Line Items]                    
Net     643   643   £ 484      
Puerto Rico                    
Schedule of Expected Losses to be Paid [Line Items]                    
Net     412   412         553
Insured financial obligations insured contractual payments outstanding, net     479   479         643
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     358   358         464
Insured financial obligations insured contractual payments outstanding, net     412   412         537
Puerto Rico | Other Puerto Rico Exposure                    
Schedule of Expected Losses to be Paid [Line Items]                    
Net     $ 41   $ 41         $ 76
United States | RMBS | First Lien                    
Schedule of Expected Losses to be Paid [Line Items]                    
Number of delinquent payments | Payment         2          
Projected loss assumptions, period to reach final loss severity rate         4 years          
Deferred loan balances to be recovered, least stressful environment, percent     80.00%   80.00%   80.00% 80.00%    
United States | RMBS | First Lien | More Stressful Environment                    
Schedule of Expected Losses to be Paid [Line Items]                    
Percent of deferred loan balances to be recovered         20.00%          
Projected loss assumptions, period to reach final loss severity rate         9 years          
Period from plateau to intermediate conditional default rate (in months)         16 months          
Period conditional default rate held constant         42 months          
Projected loss assumptions, increase (decrease) in expected loss to be paid, net         $ 34          
United States | RMBS | First Lien | Least Stressful Environment                    
Schedule of Expected Losses to be Paid [Line Items]                    
Period from plateau to intermediate conditional default rate (in months)         8 months          
Projected loss assumptions, increase (decrease) in expected loss to be paid, net         $ (28)          
Projected loss assumptions, CDR, plateau rate, projection period         30 months          
United States | RMBS | Second Lien                    
Schedule of Expected Losses to be Paid [Line Items]                    
Percent of deferred loan balances to be recovered         2.00%          
Projected loss assumptions, period of consistent conditional default rate         5 years          
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         40.00%          
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 | Home Equity Line of Credit                    
Schedule of Expected Losses to be Paid [Line Items]                    
Change in estimate for increased conditional default rate plateau period         $ 43          
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         $ 43