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Variable Interest Entities (Summary Of Nonconsolidated VIEs Assets And Liabilities) (Detail) - USD ($) $ in Millions | Sep. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss | $ 4,911 | $ 5,526
Carrying Value of VIE Assets | 6,551 | 7,284
Carrying Value of VIE Liabilities | 6,308 | 6,445
Investments [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 21 | 15
Premiums Receivable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 29 | 34
Insurance Loss Recoverable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 563 | 781
Unearned Premium Revenue [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 29 | 33
Loss And Loss Adjustment Expense Reserves Member [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 515 | 447
Global Structured Finance [Member] |  |
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss | 3,021 | 3,600
Global Structured Finance [Member] | Investments [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 21 | 15
Global Structured Finance [Member] | Premiums Receivable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 23 | 26
Global Structured Finance [Member] | Insurance Loss Recoverable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 563 | 781
Global Structured Finance [Member] | Unearned Premium Revenue [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 22 | 24
Global Structured Finance [Member] | Loss And Loss Adjustment Expense Reserves Member [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 514 | 447
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] |  |
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss | 1,921 | 2,253
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Investments [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 21 | 15
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Premiums Receivable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 17 | 19
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Insurance Loss Recoverable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 104 | 107
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Unearned Premium Revenue [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 15 | 16
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Loss And Loss Adjustment Expense Reserves Member [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 495 | 436
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] |  |
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss |  | 26
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] | Investments [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets |  | 0
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] | Premiums Receivable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets |  | 0
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] | Insurance Loss Recoverable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets |  | 0
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] | Unearned Premium Revenue [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities |  | 0
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] | Loss And Loss Adjustment Expense Reserves Member [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities |  | 0
Global Structured Finance [Member] | Consumer Asset Backed [Member] |  |
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss | 313 | 384
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 | 1 | 1
Global Structured Finance [Member] | Consumer Asset Backed [Member] | Insurance Loss Recoverable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 1 | 1
Global Structured Finance [Member] | Consumer Asset Backed [Member] | Unearned Premium Revenue [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 1 | 1
Global Structured Finance [Member] | Consumer Asset Backed [Member] | Loss And Loss Adjustment Expense Reserves Member [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 17 | 11
Global Structured Finance [Member] | Corporate Asset Backed [Member] |  |
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss | 787 | 937
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 | 5 | 6
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Insurance Loss Recoverable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 458 | 673
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Unearned Premium Revenue [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 6 | 7
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Loss And Loss Adjustment Expense Reserves Member [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 2 | 0
Global Public Finance [Member] |  |
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss | 1,890 | 1,926
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 | 6 | 8
Global Public Finance [Member] | Insurance Loss Recoverable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 0 | 0
Global Public Finance [Member] | Unearned Premium Revenue [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 7 | 9
Global Public Finance [Member] | Loss And Loss Adjustment Expense Reserves Member [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | $ 1 | $ 0

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