Variable Interest Entities (Summary Of Nonconsolidated VIEs Assets And Liabilities) (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	$ 3,228	$ 4,297
Carrying Value of VIE Assets	5,252	5,751
Carrying Value of VIE Liabilities	5,275	5,602
Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	87	21
Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	25	29
Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	335	455
Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	24	27
Loss And Loss Adjustment Expense Reserves Member [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	448	499
Global Structured Finance [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	2,178	2,863
Global Structured Finance [Member] \| Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	87	21
Global Structured Finance [Member] \| Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	19	22
Global Structured Finance [Member] \| Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	335	455
Global Structured Finance [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	18	20
Global Structured Finance [Member] \| Loss And Loss Adjustment Expense Reserves Member [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	448	497
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	1,383	1,835
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	87	21
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	14	16
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	45	90
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	12	14
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	434	482
Global Structured Finance [Member] \| Consumer Asset Backed [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	261	293
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	11	15
Global Structured Finance [Member] \| Corporate Asset Backed [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	534	735
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	4	5
Global Structured Finance [Member] \| Corporate Asset Backed [Member] \| Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	289	364
Global Structured Finance [Member] \| Corporate Asset Backed [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	5	5
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	3	0
Global Public Finance [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	1,050	1,434
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	7
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	6	7
Global Public Finance [Member] \| Loss And Loss Adjustment Expense Reserves Member [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	$ 0	$ 2

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Sum of the carrying amounts as of the balance sheet date of all liabilities that are recognized. Liabilities are probable future sacrifices of economic benefits arising from present obligations of an entity to transfer assets or provide services to other entities in the future.

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The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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