Loss and Loss Adjustment Expense Reserves (Schedule of Losses and Loss Adjustment Expenses Reserves and Recoveries) (Detail) - USD ($) $ in Millions		Sep. 30, 2022		Dec. 31, 2021
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves	[1]	$ 1,047	[2]	$ 894	[3]
Insurance Loss Recoverable [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		273		1,296
Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		273		1,296
Loss and loss adjustment expense reserves		1,047		894
US Public Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		242		1,054
Loss and loss adjustment expense reserves	[1]	688		425
International And Structured Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		33		244
Loss and loss adjustment expense reserves	[1]	568		687
International And Structured Finance Insurance [Member] | Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		31		242
Loss and loss adjustment expense reserves	[1]	359		469
Consolidation Elimination [Member] | International And Structured Finance Insurance [Member] | Variable Interest Entity Primary Beneficiary [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		(2)		(2)
Loss and loss adjustment expense reserves	[1]	$ (209)		$ (218)

[1] Amounts are net of estimated recoveries of expected future claims.

[2] Includes changes in amount and timing of estimated payments and recoveries.

[3] Amount is net of recoveries received on claims not yet paid.