v3.25.2
Variable Interest Entities (Summary of Nonconsolidated VIEs Assets and Liabilities) (Detail) - USD ($)
$ in Millions
Jun. 30, 2025
Dec. 31, 2024
Jun. 30, 2024
Variable Interest Entity [Line Items]      
Maximum Exposure to Loss $ 1,255 $ 1,425  
Carrying Value of VIE Assets 2,134 2,168 $ 2,304
Carrying Value of VIE Liabilities 4,299 4,244  
Unearned Premium Revenue [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Liabilities 7 8  
Loss And Loss Adjustment Expense Reserves [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Liabilities 231 227  
Investments [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 29 26  
Premiums Receivable [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 9 10  
Insurance Loss Recoverable [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 21 21  
Global Structured Finance [Member]      
Variable Interest Entity [Line Items]      
Maximum Exposure to Loss 1,056 1,229  
Global Structured Finance [Member] | Unearned Premium Revenue [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Liabilities 5 5  
Global Structured Finance [Member] | Loss And Loss Adjustment Expense Reserves [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Liabilities 231 227  
Global Structured Finance [Member] | Investments [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 29 26  
Global Structured Finance [Member] | Premiums Receivable [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 6 7  
Global Structured Finance [Member] | Insurance Loss Recoverable [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 21 21  
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member]      
Variable Interest Entity [Line Items]      
Maximum Exposure to Loss 756 785  
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Unearned Premium Revenue [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Liabilities 3 3  
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Loss And Loss Adjustment Expense Reserves [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Liabilities 229 224  
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Investments [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 29 26  
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Premiums Receivable [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 4 5  
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Insurance Loss Recoverable [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 21 21  
Global Structured Finance [Member] | Consumer Asset Backed [Member]      
Variable Interest Entity [Line Items]      
Maximum Exposure to Loss 71 86  
Global Structured Finance [Member] | Consumer Asset Backed [Member] | Unearned Premium Revenue [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Liabilities 0 0  
Global Structured Finance [Member] | Consumer Asset Backed [Member] | Loss And Loss Adjustment Expense Reserves [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Liabilities 2 3  
Global Structured Finance [Member] | Consumer Asset Backed [Member] | Investments [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 0 0  
Global Structured Finance [Member] | Consumer Asset Backed [Member] | Premiums Receivable [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 0 0  
Global Structured Finance [Member] | Consumer Asset Backed [Member] | Insurance Loss Recoverable [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 0 0  
Global Structured Finance [Member] | Corporate Asset Backed [Member]      
Variable Interest Entity [Line Items]      
Maximum Exposure to Loss 229 358  
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Unearned Premium Revenue [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Liabilities 2 2  
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Loss And Loss Adjustment Expense Reserves [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Liabilities 0 0  
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Investments [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 0 0  
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Premiums Receivable [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 2 2  
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Insurance Loss Recoverable [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 0 0  
Global Public Finance [Member]      
Variable Interest Entity [Line Items]      
Maximum Exposure to Loss 199 196  
Global Public Finance [Member] | Unearned Premium Revenue [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Liabilities 2 3  
Global Public Finance [Member] | Loss And Loss Adjustment Expense Reserves [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Liabilities 0 0  
Global Public Finance [Member] | Investments [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 0 0  
Global Public Finance [Member] | Premiums Receivable [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets 3 3  
Global Public Finance [Member] | Insurance Loss Recoverable [Member]      
Variable Interest Entity [Line Items]      
Carrying Value of VIE Assets $ 0 $ 0