Variable Interest Entities (Summary of Nonconsolidated VIEs Assets and Liabilities) (Detail) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	$ 2,527	$ 2,824
Carrying Value of VIE Assets	4,015	4,696
Carrying Value of VIE Liabilities	4,864	4,996
Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	110	87
Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	21	24
Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	31	241
Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	18	21
Loss And Loss Adjustment Expense Reserves Member [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	344	447
Global Structured Finance [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	1,805	1,990
Global Structured Finance [Member] \| Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	110	87
Global Structured Finance [Member] \| Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	16	18
Global Structured Finance [Member] \| Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	31	241
Global Structured Finance [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	13	16
Global Structured Finance [Member] \| Loss And Loss Adjustment Expense Reserves Member [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	344	447
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	1,165	1,261
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	110	87
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	13	14
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	24	40
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	10	11
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	338	430
Global Structured Finance [Member] \| Consumer Asset Backed [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	177	226
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	1
Global Structured Finance [Member] \| Consumer Asset Backed [Member] \| Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	0	1
Global Structured Finance [Member] \| Consumer Asset Backed [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	0	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	5	6
Global Structured Finance [Member] \| Corporate Asset Backed [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	463	503
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	3	3
Global Structured Finance [Member] \| Corporate Asset Backed [Member] \| Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	7	200
Global Structured Finance [Member] \| Corporate Asset Backed [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	3	4
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	1	11
Global Public Finance [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	722	834
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	5	6
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	5	5
Global Public Finance [Member] \| Loss And Loss Adjustment Expense Reserves Member [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	$ 0	$ 0

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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