v3.26.1
Expected Loss to be Paid (Recovered) - Additional Information (Details)
€ in Millions, £ in Millions, $ in Millions
 1 Months Ended 3 Months Ended 6 Months Ended
Sep. 18, 2025
board_member
Aug. 31, 2025
board_member
Jun. 30, 2026
USD ($)
Jun. 30, 2025
USD ($)
Jun. 30, 2026
USD ($)
Payment
Jun. 30, 2025
USD ($)
Jun. 30, 2026
GBP (£)
Jun. 30, 2026
EUR (€)
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     $ 2 $ 5 $ 4 $ (56)      
Expected LAE to be paid     9   9       $ 8
Credit for estimated future recoveries of claims paid     302   302       311
Net     281,400   281,400       277,100
Insured financial obligations insured contractual payments outstanding, net     446,600   446,600       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                
BIG                  
Schedule of Expected Losses to be Paid [Line Items]                  
Net     8,500   8,500       8,760
European Renewable Energy | BIG                  
Schedule of Expected Losses to be Paid [Line Items]                  
Net     831   831     € 727  
Thames Water Utilities Finance PLC | BIG                  
Schedule of Expected Losses to be Paid [Line Items]                  
Net     2,400   2,400   £ 1,800    
U.K. Student Accommodations | BIG                  
Schedule of Expected Losses to be Paid [Line Items]                  
Net     385   385   291    
U.K. National Health Service Trusts | BIG                  
Schedule of Expected Losses to be Paid [Line Items]                  
Net     643   643   £ 484    
U.S. Transportation | BIG                  
Schedule of Expected Losses to be Paid [Line Items]                  
Net     $ 1,100   $ 1,100        
United States | RMBS | First Lien                  
Schedule of Expected Losses to be Paid [Line Items]                  
Number of delinquent payments | Payment         2        
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         $ 31        
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         $ (30)        
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         $ 45        
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         45        
Puerto Rico                  
Schedule of Expected Losses to be Paid [Line Items]                  
Net     $ 553   553       553
Insured financial obligations insured contractual payments outstanding, net     630   630       643
Puerto Rico | Other Puerto Rico Exposure                  
Schedule of Expected Losses to be Paid [Line Items]                  
Net     76   76       76
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     464   464       464
Insured financial obligations insured contractual payments outstanding, net     $ 526   $ 526       $ 537