Variable Interest Entities (Summary of Nonconsolidated VIEs Assets and Liabilities) (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	$ 1,550	$ 1,594
Carrying Value of VIE Assets	2,488	2,606
Carrying Value of VIE Liabilities	4,211	4,253
Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	19	19
Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	11	11
Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	29	31
Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	9	10
Loss And Loss Adjustment Expense Reserves [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	235	242
Global Structured Finance [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	1,340	1,376
Global Structured Finance [Member] \| Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	19	19
Global Structured Finance [Member] \| Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	7	7
Global Structured Finance [Member] \| Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	29	31
Global Structured Finance [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	6	6
Global Structured Finance [Member] \| Loss And Loss Adjustment Expense Reserves [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	235	242
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	838	853
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Investments [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	19	19
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Premiums Receivable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	5	5
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Insurance Loss Recoverable [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Assets	21	23
Global Structured Finance [Member] \| Residential Mortgage Backed Securities [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	3	3
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	232	239
Global Structured Finance [Member] \| Consumer Asset Backed [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	111	121
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	1
Global Structured Finance [Member] \| Consumer Asset Backed [Member] \| Unearned Premium Revenue [Member]
Variable Interest Entity [Line Items]
Carrying Value of VIE Liabilities	0	0
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	3
Global Structured Finance [Member] \| Corporate Asset Backed [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	391	402
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	2
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 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 Public Finance [Member]
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	210	218
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	4
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	3	4
Global Public Finance [Member] \| Loss And Loss Adjustment Expense Reserves [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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