v3.24.1.u1
Fair Value Measurements - Financial Assets and Liabilities Carried at Fair Value (Details) - USD ($)
$ in Millions
Mar. 31, 2024
Dec. 31, 2023
Financial assets at fair value:    
Equity securities $ 39 $ 51
Recurring    
Financial assets at fair value:    
Equity securities 39 51
Short-term investments 374 206
Debt Securities, including held for sale assets 9,480 9,855
Recurring | Forwards, swaps, options    
Financial assets at fair value:    
Derivative assets 147 132
Liabilities, Fair Value Disclosure [Abstract]    
Derivative liabilities 4 4
Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring    
Financial assets at fair value:    
Equity securities 2 4
Short-term investments 0 0
Debt Securities, including held for sale assets 165 130
Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring | Forwards, swaps, options    
Financial assets at fair value:    
Derivative assets 0 0
Liabilities, Fair Value Disclosure [Abstract]    
Derivative liabilities 0 0
Significant Other Observable Inputs (Level 2) | Recurring    
Financial assets at fair value:    
Equity securities 37 47
Short-term investments 374 206
Debt Securities, including held for sale assets 8,893 9,278
Significant Other Observable Inputs (Level 2) | Recurring | Forwards, swaps, options    
Financial assets at fair value:    
Derivative assets 147 131
Liabilities, Fair Value Disclosure [Abstract]    
Derivative liabilities 4 4
Significant Unobservable Inputs (Level 3) | Recurring    
Financial assets at fair value:    
Equity securities 0 0
Short-term investments 0 0
Debt Securities, including held for sale assets 422 447
Significant Unobservable Inputs (Level 3) | Recurring | Forwards, swaps, options    
Financial assets at fair value:    
Derivative assets 0 1
Liabilities, Fair Value Disclosure [Abstract]    
Derivative liabilities 0 0
Federal government and agency | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 300 267
Federal government and agency | Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 165 130
Federal government and agency | Significant Other Observable Inputs (Level 2) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 135 137
Federal government and agency | Significant Unobservable Inputs (Level 3) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 0 0
State and local government | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 38 38
State and local government | Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 0 0
State and local government | Significant Other Observable Inputs (Level 2) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 38 38
State and local government | Significant Unobservable Inputs (Level 3) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 0 0
Foreign government | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 348 352
Foreign government | Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 0 0
Foreign government | Significant Other Observable Inputs (Level 2) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 348 352
Foreign government | Significant Unobservable Inputs (Level 3) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 0 0
Corporate | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 8,441 8,833
Corporate | Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 0 0
Corporate | Significant Other Observable Inputs (Level 2) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 8,072 8,432
Corporate | Significant Unobservable Inputs (Level 3) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 369 401
Mortgage and other asset-backed | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 353 365
Mortgage and other asset-backed | Quoted Prices in Active Markets for Identical Assets (Level 1) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 0 0
Mortgage and other asset-backed | Significant Other Observable Inputs (Level 2) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets 300 319
Mortgage and other asset-backed | Significant Unobservable Inputs (Level 3) | Recurring    
Financial assets at fair value:    
Debt Securities, including held for sale assets $ 53 $ 46