v3.26.3
Fair Value Measurement - Fair Value Level 3 Rollforward Recurring Basis (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
FG VIEs’ Assets        
Fair Value Level 3 Rollforward        
Fair value at beginning of period $ 143 $ 153 $ 150 $ 147
Assured Life Re Acquisition-measurement period adjustment 0      
Assured Life Re Acquisition     0  
Total pre-tax realized and unrealized gains (losses) recorded in:        
Net income (loss) (1) 7 2 14
Other comprehensive income (loss) 0 0 0 0
Purchases 0 0 0 0
Sales 0 0 0 0
Settlements (4) (6) (14) (16)
Consolidations       9
Deconsolidations (9)   0 (9)
Transfers into Level 3 0   0  
Fair value at end of period 138 145 138 145
Change in unrealized gains/(losses) related to financial instruments held (2) 6 0 11
Assets of CIVs        
Fair Value Level 3 Rollforward        
Fair value at beginning of period   121 167 99
Assured Life Re Acquisition     0  
Total pre-tax realized and unrealized gains (losses) recorded in:        
Net income (loss)   11 4 33
Other comprehensive income (loss)   0 0 0
Purchases   0 0 0
Sales   0 0 0
Settlements   0 (165) 0
Consolidations       0
Deconsolidations 0   (6) 0
Transfers into Level 3     0  
Fair value at end of period 0 132 0 132
Change in unrealized gains/(losses) related to financial instruments held   11 0 33
Other        
Fair Value Level 3 Rollforward        
Fair value at beginning of period 22 5 24 5
Assured Life Re Acquisition-measurement period adjustment 0      
Assured Life Re Acquisition     0  
Total pre-tax realized and unrealized gains (losses) recorded in:        
Net income (loss) (1) 9 (3) 10
Other comprehensive income (loss) (1) 1 (1) 0
Purchases 0 0 0 0
Sales 0 0 0 0
Settlements 0 0 0 0
Consolidations       0
Deconsolidations 0   0 0
Transfers into Level 3 0   0  
Fair value at end of period 20 15 20 15
Change in unrealized gains/(losses) related to financial instruments held (1) 9 (3) 10
Other | Location, Statement of Other Comprehensive Income, Balance [Axis]: us-gaap:OtherComprehensiveIncomeLossNetOfTax        
Total pre-tax realized and unrealized gains (losses) recorded in:        
Change in unrealized gains/(losses) related to financial instruments held (1) 1 (1) 0
Financial Guaranty Variable Interest Entities        
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]        
Fair value at start of period (147) (161) (156) (164)
Total pre-tax realized and unrealized gains (losses) recorded in:        
Net income (loss) 3 (4) 2 (9)
Other comprehensive income (loss) 0 1 2 1
Settlements 4 5 12 13
Fair value at end of period (140) (159) (140) (159)
Change in unrealized gains/(losses) included in earnings related to financial instruments 3 (4) 3 (8)
Change in unrealized gains/(losses) included in OCI related to financial instruments 1 1 3 1
Obligations of state and political subdivisions | Fixed-maturity securities, available-for-sale:        
Fair Value Level 3 Rollforward        
Fair value at beginning of period 10 10 10 10
Assured Life Re Acquisition-measurement period adjustment 0      
Assured Life Re Acquisition     0  
Total pre-tax realized and unrealized gains (losses) recorded in:        
Net income (loss) 0 0 0 2
Other comprehensive income (loss) 0 0 0 0
Purchases 0 0 0 0
Sales 0 0 0 0
Settlements (1) 0 (1) (2)
Consolidations       0
Deconsolidations 0   0 0
Transfers into Level 3 0   0  
Fair value at end of period 9 10 9 10
Obligations of state and political subdivisions | Fixed-maturity securities, available-for-sale: | Location, Statement of Other Comprehensive Income, Balance [Axis]: us-gaap:OtherComprehensiveIncomeLossNetOfTax        
Total pre-tax realized and unrealized gains (losses) recorded in:        
Change in unrealized gains/(losses) related to financial instruments held 0 0 0 0
Corporate securities | Fixed-maturity securities, available-for-sale:        
Fair Value Level 3 Rollforward        
Fair value at beginning of period 160 84 168 0
Assured Life Re Acquisition-measurement period adjustment 0      
Assured Life Re Acquisition     0  
Total pre-tax realized and unrealized gains (losses) recorded in:        
Net income (loss) 1 1 3 1
Other comprehensive income (loss) (3) 10 (13) 20
Purchases 0 73 0 147
Sales 0 0 0 0
Settlements 0 0 0 0
Consolidations       0
Deconsolidations 0   0 0
Transfers into Level 3 0   0  
Fair value at end of period 158 168 158 168
Corporate securities | Fixed-maturity securities, available-for-sale: | Location, Statement of Other Comprehensive Income, Balance [Axis]: us-gaap:OtherComprehensiveIncomeLossNetOfTax        
Total pre-tax realized and unrealized gains (losses) recorded in:        
Change in unrealized gains/(losses) related to financial instruments held (3) 10 (13) 20
RMBS | Fixed-maturity securities, available-for-sale:        
Fair Value Level 3 Rollforward        
Fair value at beginning of period 155 142 144 145
Assured Life Re Acquisition-measurement period adjustment 0      
Assured Life Re Acquisition     0  
Total pre-tax realized and unrealized gains (losses) recorded in:        
Net income (loss) 2 3 6 7
Other comprehensive income (loss) (4) 6 12 12
Purchases 0 0 2 0
Sales 0 0 0 0
Settlements (6) (6) (17) (19)
Consolidations       0
Deconsolidations 0   0 0
Transfers into Level 3 0   0  
Fair value at end of period 147 145 147 145
RMBS | Fixed-maturity securities, available-for-sale: | Location, Statement of Other Comprehensive Income, Balance [Axis]: us-gaap:OtherComprehensiveIncomeLossNetOfTax        
Total pre-tax realized and unrealized gains (losses) recorded in:        
Change in unrealized gains/(losses) related to financial instruments held (4) 6 12 12
CMBS | Fixed-maturity securities, available-for-sale:        
Fair Value Level 3 Rollforward        
Fair value at beginning of period 0   0  
Assured Life Re Acquisition-measurement period adjustment 0      
Assured Life Re Acquisition     0  
Total pre-tax realized and unrealized gains (losses) recorded in:        
Net income (loss) 0   0  
Other comprehensive income (loss) 0   0  
Purchases 0   0  
Sales 0   0  
Settlements 0   0  
Deconsolidations     0  
Transfers into Level 3 17   17  
Fair value at end of period 17   17  
CMBS | Fixed-maturity securities, available-for-sale: | Location, Statement of Other Comprehensive Income, Balance [Axis]: us-gaap:OtherComprehensiveIncomeLossNetOfTax        
Total pre-tax realized and unrealized gains (losses) recorded in:        
Change in unrealized gains/(losses) related to financial instruments held 0   0  
Asset-backed securities | Fixed-maturity securities, available-for-sale:        
Fair Value Level 3 Rollforward        
Fair value at beginning of period 463 977 511 1,031
Assured Life Re Acquisition-measurement period adjustment 0      
Assured Life Re Acquisition     0  
Total pre-tax realized and unrealized gains (losses) recorded in:        
Net income (loss) 3 3 1 21
Other comprehensive income (loss) (3) (3) (29) 8
Purchases 52 40 114 40
Sales (2) 0 (2) (12)
Settlements (29) (496) (111) (567)
Consolidations       0
Deconsolidations 0   0 0
Transfers into Level 3 0   0  
Fair value at end of period 484 521 484 521
Asset-backed securities | Fixed-maturity securities, available-for-sale: | Location, Statement of Other Comprehensive Income, Balance [Axis]: us-gaap:OtherComprehensiveIncomeLossNetOfTax        
Total pre-tax realized and unrealized gains (losses) recorded in:        
Change in unrealized gains/(losses) related to financial instruments held (3) (2) (29) (20)
Fixed-Maturity Securities, Trading | Fixed-maturity securities, available-for-sale:        
Fair Value Level 3 Rollforward        
Fair value at beginning of period 4 4 4 5
Assured Life Re Acquisition-measurement period adjustment 0      
Assured Life Re Acquisition     0  
Total pre-tax realized and unrealized gains (losses) recorded in:        
Net income (loss) 0 1 0 1
Other comprehensive income (loss) 0 0 0 0
Purchases 0 0 0 0
Sales 0 0 0 0
Settlements (1) (1) (6) (2)
Consolidations       0
Deconsolidations 0   0 0
Transfers into Level 3 0   5  
Fair value at end of period 3 4 3 4
Change in unrealized gains/(losses) related to financial instruments held 0 0 (1) 0
Funds Withheld        
Fair Value Level 3 Rollforward        
Fair value at beginning of period 296   0  
Assured Life Re Acquisition-measurement period adjustment (6)      
Assured Life Re Acquisition     287  
Total pre-tax realized and unrealized gains (losses) recorded in:        
Net income (loss) 2   9  
Other comprehensive income (loss) 0   0  
Purchases 0   0  
Sales 0   (29)  
Settlements (25)   0  
Deconsolidations     0  
Transfers into Level 3 0   0  
Fair value at end of period 267   267  
Change in unrealized gains/(losses) related to financial instruments held 2   9  
Credit Risk Contract        
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]        
Fair value at start of period (14) (29) (15) (29)
Total pre-tax realized and unrealized gains (losses) recorded in:        
Net income (loss) 2 5 5 110
Other comprehensive income (loss) 0 0 0 0
Settlements (2) (2) (4) (107)
Fair value at end of period (14) (26) (14) (26)
Change in unrealized gains/(losses) included in earnings related to financial instruments $ 1 $ 3 $ 1 $ 3