v3.26.1
Expected Loss to be Paid (Recovered) - Net Expected Loss to be Paid After Net Expected Recoveries for Breaches of R&W Rollforward (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]          
Net expected loss to be paid (recovered), beginning of period $ 141 $ 150 $ 101 $ 106 $ 106
Accretion of discount 2 2 4 3  
Changes in discount rates (2) 1 (6) 6  
Changes in timing and assumptions 48 33 94 12  
Total economic loss development (benefit) 48 36 92 21  
Net (paid) recovered losses 3 0 (1) 59  
Net expected loss to be paid (recovered), end of period 192 186 192 $ 186 101
Period after the end of the reporting period within which the ceded paid losses are typically settled (in days)       45 days  
Public finance          
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]          
Net expected loss to be paid (recovered), beginning of period 131 157 95 $ 116 116
Total economic loss development (benefit) 48 42 95 95  
Net (paid) recovered losses (5) (7) (16) (19)  
Net expected loss to be paid (recovered), end of period 174 192 174 192 95
Other structured finance          
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]          
Net expected loss to be paid (recovered), beginning of period 58 30 60 33 33
Total economic loss development (benefit) 1 0 0 (65)  
Net (paid) recovered losses (1) (1) (2) 61  
Net expected loss to be paid (recovered), end of period 58 29 58 29 60
Structured finance          
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]          
Net expected loss to be paid (recovered), beginning of period 10 (7) 6 (10) (10)
Total economic loss development (benefit) 0 (6) (3) (74)  
Net (paid) recovered losses 8 7 15 78  
Net expected loss to be paid (recovered), end of period 18 (6) $ 18 (6) $ 6
Minimum          
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]          
Risk free discount rate     2.18%   1.93%
Maximum          
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]          
Risk free discount rate     5.67%   5.35%
Weighted Average          
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]          
Risk free discount rate     4.35%   3.92%
United States | Public finance          
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]          
Net expected loss to be paid (recovered), beginning of period 3 35 $ (31) 18 $ 18
Total economic loss development (benefit) 44 24 89 53  
Net (paid) recovered losses (5) (6) (16) (18)  
Net expected loss to be paid (recovered), end of period 42 53 42 53 (31)
United States | RMBS          
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]          
Net expected loss to be paid (recovered), beginning of period (48) (37) (54) (43) (43)
Changes in discount rates 0 (2) 0 (1)  
Total economic loss development (benefit) (1) (6) (3) (9)  
Net (paid) recovered losses 9 8 17 17  
Net expected loss to be paid (recovered), end of period (40) (35) (40) (35) (54)
Non-U.S. public finance | Public finance          
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]          
Net expected loss to be paid (recovered), beginning of period 128 122 126 98 98
Total economic loss development (benefit) 4 18 6 42  
Net (paid) recovered losses 0 (1) 0 (1)  
Net expected loss to be paid (recovered), end of period $ 132 $ 139 $ 132 $ 139 $ 126