Variable Interest Entities (Summary of Nonconsolidated VIEs Assets and Liabilities) (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	$ 1,594	$ 1,840
Carrying Value of VIE Assets	2,606	3,375
Carrying Value of VIE Liabilities	4,253	4,251
Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	10	12
Loss And Loss Adjustment Expense Reserves [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	242	282
Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	19	75
Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	11	14
Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	31	28
Global Structured Finance [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	1,376	1,610
Global Structured Finance [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	6	8
Global Structured Finance [Member] \| Loss And Loss Adjustment Expense Reserves [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	242	282
Global Structured Finance [Member] \| Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	19	75
Global Structured Finance [Member] \| Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	7	9
Global Structured Finance [Member] \| Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	31	28
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	853	996
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	3	4
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	239	277
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	19	75
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	5	6
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	23	21
Global Structured Finance [Member] \| Consumer Asset Backed [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	121	164
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]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	3	5
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	1	0
Global Structured Finance [Member] \| Corporate Asset Backed [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	402	450
Global Structured Finance [Member] \| Corporate Asset Backed [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	3	3
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	3
Global Structured Finance [Member] \| Corporate Asset Backed [Member] \| Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	7	7
Global Public Finance [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	218	230
Global Public Finance [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	4	4
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	4	5
Global Public Finance [Member] \| Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	$ 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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