v3.26.1
Fair Value Measurements - Fair Value by Hierarchy (Details) - USD ($)
$ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2026
Dec. 31, 2025
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale $ 45,824 $ 46,041
Fixed maturities, at fair value using the fair value option ("FVO Securities") 125 168
Equity securities, at fair value [1] 560 422
Derivative assets (3) (20)
Short-term investments 3,866 4,004
Total assets accounted for at fair value on a recurring basis [3] 50,372 50,655
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities 10 20
Total liabilities accounted for at fair value on a recurring basis $ 10 $ 20
Equity Security, FV-NI, Contractual Sale Restriction, Nature of Restriction and Circumstance for Lapse Level 3 includes investments that have contractual sales restrictions that require consent to sell and are in place for the duration that the securities are held by the Company. Level 3 includes investments that have contractual sales restrictions that require consent to sell and are in place for the duration that the securities are held by the Company.
Credit derivatives    
Assets accounted for at fair value on a recurring basis    
Derivative assets $ 14  
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities (14)  
Foreign exchange derivatives    
Assets accounted for at fair value on a recurring basis    
Derivative assets (11) $ (20)
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities (6) 17
Interest rate derivatives    
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities 10 3
Quoted Prices in
Active Markets
for Identical
Assets
(Level 1)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 489 164
Fixed maturities, at fair value using the fair value option ("FVO Securities") 0 0
Equity securities, at fair value [1] 430 311
Derivative assets 0 0
Short-term investments 245 491
Total assets accounted for at fair value on a recurring basis [3] 1,164 966
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities 0 0
Total liabilities accounted for at fair value on a recurring basis 0 0
Quoted Prices in
Active Markets
for Identical
Assets
(Level 1) | Credit derivatives    
Assets accounted for at fair value on a recurring basis    
Derivative assets 0  
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities 0  
Quoted Prices in
Active Markets
for Identical
Assets
(Level 1) | Foreign exchange derivatives    
Assets accounted for at fair value on a recurring basis    
Derivative assets 0 0
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities 0 0
Quoted Prices in
Active Markets
for Identical
Assets
(Level 1) | Interest rate derivatives    
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities 0 0
Significant
Observable
Inputs
(Level 2)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 41,932 42,505
Fixed maturities, at fair value using the fair value option ("FVO Securities") 0 0
Equity securities, at fair value [1] 6 5
Derivative assets (3) (20)
Short-term investments 2,912 3,131
Total assets accounted for at fair value on a recurring basis [3] 44,847 45,661
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities 10 20
Total liabilities accounted for at fair value on a recurring basis 10 20
Significant
Observable
Inputs
(Level 2) | Credit derivatives    
Assets accounted for at fair value on a recurring basis    
Derivative assets 14  
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities (14)  
Significant
Observable
Inputs
(Level 2) | Foreign exchange derivatives    
Assets accounted for at fair value on a recurring basis    
Derivative assets (11) (20)
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities (6) 17
Significant
Observable
Inputs
(Level 2) | Interest rate derivatives    
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities 10 3
Fair Value, Inputs, Level 3 [Member]    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 3,403 3,372
Fixed maturities, at fair value using the fair value option ("FVO Securities") 125 168
Equity securities, at fair value [1] 124 106
Derivative assets 0 0
Short-term investments 709 382
Total assets accounted for at fair value on a recurring basis [3] 4,361 4,028
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities 0 0
Total liabilities accounted for at fair value on a recurring basis 0 0
Fair Value, Inputs, Level 3 [Member] | Credit derivatives    
Assets accounted for at fair value on a recurring basis    
Derivative assets 0  
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities 0  
Fair Value, Inputs, Level 3 [Member] | Foreign exchange derivatives    
Assets accounted for at fair value on a recurring basis    
Derivative assets 0 0
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities 0 0
Fair Value, Inputs, Level 3 [Member] | Interest rate derivatives    
Liabilities accounted for at fair value on a recurring basis    
Derivative liabilities 0 0
Fair Value Measured at Net Asset Value Per Share [Member]    
Liabilities accounted for at fair value on a recurring basis    
Deposit Assets 84 87
Asset-backed securities ("ABS")    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 4,783 4,663
Asset-backed securities ("ABS") | Quoted Prices in
Active Markets
for Identical
Assets
(Level 1)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 0 0
Asset-backed securities ("ABS") | Significant
Observable
Inputs
(Level 2)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 4,608 4,496
Asset-backed securities ("ABS") | Fair Value, Inputs, Level 3 [Member]    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 175 167
Collateralized Loan Obligations [Member]    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 3,360 3,316
Fixed maturities, at fair value using the fair value option ("FVO Securities") 125 168
Collateralized Loan Obligations [Member] | Quoted Prices in
Active Markets
for Identical
Assets
(Level 1)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 0 0
Collateralized Loan Obligations [Member] | Significant
Observable
Inputs
(Level 2)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 3,160 3,099
Collateralized Loan Obligations [Member] | Fair Value, Inputs, Level 3 [Member]    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 200 217
CMBS    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 1,822 2,328
CMBS | Quoted Prices in
Active Markets
for Identical
Assets
(Level 1)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 0 0
CMBS | Significant
Observable
Inputs
(Level 2)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 1,725 2,213
CMBS | Fair Value, Inputs, Level 3 [Member]    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 97 115
Corporate    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 23,868 23,076
Corporate | Quoted Prices in
Active Markets
for Identical
Assets
(Level 1)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 0 0
Corporate | Significant
Observable
Inputs
(Level 2)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 20,952 20,210
Corporate | Fair Value, Inputs, Level 3 [Member]    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 2,916 2,866
Foreign government/government agencies    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 454 447
Foreign government/government agencies | Quoted Prices in
Active Markets
for Identical
Assets
(Level 1)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 0 0
Foreign government/government agencies | Significant
Observable
Inputs
(Level 2)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 454 447
Foreign government/government agencies | Fair Value, Inputs, Level 3 [Member]    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 0 0
Municipal    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 4,105 4,652
Municipal | Quoted Prices in
Active Markets
for Identical
Assets
(Level 1)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 0 0
Municipal | Significant
Observable
Inputs
(Level 2)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 4,105 4,652
Municipal | Fair Value, Inputs, Level 3 [Member]    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 0 0
RMBS    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 5,787 6,178
RMBS | Quoted Prices in
Active Markets
for Identical
Assets
(Level 1)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 0 0
RMBS | Significant
Observable
Inputs
(Level 2)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 5,772 6,171
RMBS | Fair Value, Inputs, Level 3 [Member]    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 15 7
U.S. Treasuries    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 1,645 1,381
U.S. Treasuries | Quoted Prices in
Active Markets
for Identical
Assets
(Level 1)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 489 164
U.S. Treasuries | Significant
Observable
Inputs
(Level 2)    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale 1,156 1,217
U.S. Treasuries | Fair Value, Inputs, Level 3 [Member]    
Assets accounted for at fair value on a recurring basis    
Debt Securities, Available-for-Sale $ 0 $ 0