v3.26.1
Outstanding Exposure - Components of BIG Net Par Outstanding (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Dec. 31, 2025
Schedule of Insured Financial Obligations [Line Items]    
Net $ 281,400 $ 277,100
Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 268,500 265,600
Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 12,900 11,500
BIG    
Schedule of Insured Financial Obligations [Line Items]    
Net 8,500 8,760
BIG | BIG 1    
Schedule of Insured Financial Obligations [Line Items]    
Net 2,390 3,740
BIG | BIG 1 | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 2,220 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 4,940 3,810
BIG | BIG 2 | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 4,890 3,770
BIG | BIG 2 | Other structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 20 10
BIG | BIG 2 | Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 50 40
BIG | BIG 3    
Schedule of Insured Financial Obligations [Line Items]    
Net 1,170 1,210
BIG | BIG 3 | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 580 580
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 590 630
BIG | Total BIG    
Schedule of Insured Financial Obligations [Line Items]    
Net 8,500 8,760
BIG | Total BIG | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 7,690 7,920
BIG | Total BIG | Other structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 70 70
BIG | Total BIG | Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 810 840
United States | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 219,400 215,000
United States | Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 8,600 7,900
United States | BIG | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 3,400 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 1,220 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 1,600 420
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 580 580
United States | BIG | BIG 3 | RMBS    
Schedule of Insured Financial Obligations [Line Items]    
Net 540 570
United States | BIG | Total BIG | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 3,400 3,480
United States | BIG | Total BIG | RMBS    
Schedule of Insured Financial Obligations [Line Items]    
Net 740 770
Non-U.S. public finance | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 49,100 50,600
Non-U.S. public finance | Structured finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 4,300 3,600
Non-U.S. public finance | BIG | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 4,300 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 1,000 1,090
Non-U.S. public finance | BIG | BIG 2 | Public finance    
Schedule of Insured Financial Obligations [Line Items]    
Net 3,290 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 $ 4,290 $ 4,440