v3.26.3
Outstanding Exposure - Components of BIG Net Par Outstanding (Details) - USD ($)
$ in Millions
Sep. 30, 2026
Dec. 31, 2025
Schedule of Insured Financial Obligations [Line Items]    
Net $ 281,100 $ 277,100
Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 268,000 265,600
Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 13,100 11,500
BIG    
Schedule of Insured Financial Obligations [Line Items]    
Net 8,020 8,760
BIG | BIG 1    
Schedule of Insured Financial Obligations [Line Items]    
Net 3,140 3,740
BIG | BIG 1 | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 2,970 3,570
BIG | BIG 1 | Other structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 0 0
BIG | BIG 1 | Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 170 170
BIG | BIG 2    
Schedule of Insured Financial Obligations [Line Items]    
Net 3,820 3,810
BIG | BIG 2 | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 3,780 3,770
BIG | BIG 2 | Other structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 10 10
BIG | BIG 2 | Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 40 40
BIG | BIG 3    
Schedule of Insured Financial Obligations [Line Items]    
Net 1,060 1,210
BIG | BIG 3 | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 480 580
BIG | BIG 3 | Other structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 50 60
BIG | BIG 3 | Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 580 630
BIG | Total BIG    
Schedule of Insured Financial Obligations [Line Items]    
Net 8,020 8,760
BIG | Total BIG | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 7,230 7,920
BIG | Total BIG | Other structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 60 70
BIG | Total BIG | Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 790 840
United States | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 219,700 215,000
United States | Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 8,700 7,900
United States | BIG | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 3,200 3,500
United States | BIG | Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 800 900
United States | BIG | BIG 1 | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 2,290 2,480
United States | BIG | BIG 1 | RMBS    
Schedule of Insured Financial Obligations [Line Items]    
Net 170 170
United States | BIG | BIG 2 | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 460 420
United States | BIG | BIG 2 | RMBS    
Schedule of Insured Financial Obligations [Line Items]    
Net 30 30
United States | BIG | BIG 3 | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 480 580
United States | BIG | BIG 3 | RMBS    
Schedule of Insured Financial Obligations [Line Items]    
Net 530 570
United States | BIG | Total BIG | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 3,230 3,480
United States | BIG | Total BIG | RMBS    
Schedule of Insured Financial Obligations [Line Items]    
Net 730 770
Non-U.S. public finance | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 48,300 50,600
Non-U.S. public finance | Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 4,400 3,600
Non-U.S. public finance | BIG | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 4,000 4,400
Non-U.S. public finance | BIG | Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 0 0
Non-U.S. public finance | BIG | BIG 1 | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 680 1,090
Non-U.S. public finance | BIG | BIG 2 | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 3,320 3,350
Non-U.S. public finance | BIG | BIG 3 | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 0 0
Non-U.S. public finance | BIG | Total BIG | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net $ 4,000 $ 4,440