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Variable Interest Entities (Summary Of Nonconsolidated VIEs Assets And Liabilities) (Detail) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss | $ 5,526 | $ 7,284
Investments [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 15 | 17
Premiums Receivable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 34 | 40
Insurance Loss Recoverable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 781 | 987
Unearned Premium Revenue [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 33 | 41
Loss And Loss Adjustment Expense Reserves Member [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 447 | 357
Global Structured Finance [Member] |  |
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss | 3,600 | 5,053
Global Structured Finance [Member] | Investments [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 15 | 17
Global Structured Finance [Member] | Premiums Receivable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 26 | 31
Global Structured Finance [Member] | Insurance Loss Recoverable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 781 | 987
Global Structured Finance [Member] | Unearned Premium Revenue [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 24 | 29
Global Structured Finance [Member] | Loss And Loss Adjustment Expense Reserves Member [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 447 | 357
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] |  |
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss | 2,253 | 3,103
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Investments [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 15 | 17
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Premiums Receivable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 19 | 19
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Insurance Loss Recoverable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 107 | 128
Global Structured Finance [Member] | Residential Mortgage Backed Securities [Member] | Unearned Premium Revenue [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 16 | 17
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 | 436 | 345
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] |  |
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss | 26 | 52
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] | Investments [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 0 | 0
Global Structured Finance [Member] | Commercial Mortgage Backed Securities [Member] | Premiums Receivable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 0 | 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 | 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 | 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 | 0
Global Structured Finance [Member] | Consumer Asset Backed [Member] |  |
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss | 384 | 560
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 | 3
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 | 2
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 | 11 | 12
Global Structured Finance [Member] | Corporate Asset Backed [Member] |  |
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss | 937 | 1,338
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 | 6 | 9
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Insurance Loss Recoverable [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Assets | 673 | 858
Global Structured Finance [Member] | Corporate Asset Backed [Member] | Unearned Premium Revenue [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | 7 | 10
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 | 0 | 0
Global Public Finance [Member] |  |
Variable Interest Entity [Line Items] |  |
Maximum Exposure to Loss | 1,926 | 2,231
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 | 8 | 9
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 | 9 | 12
Global Public Finance [Member] | Loss And Loss Adjustment Expense Reserves Member [Member] |  |
Variable Interest Entity [Line Items] |  |
Carrying Value of VIE Liabilities | $ 0 | $ 0

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