Loss and Loss Adjustment Expense Reserves (Schedule of Losses and Loss Adjustment Expenses Reserves and Recoveries) (Detail) - USD ($) $ in Millions		Dec. 31, 2023		Dec. 31, 2022		Dec. 31, 2021
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		$ 473	[1]	$ 439	[1]	$ 894
Insurance Loss Recoverable [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		183		137		$ 1,296
Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		183		137
Loss and loss adjustment expense reserves		473		439
US Public Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		152		107
Loss and loss adjustment expense reserves	[1]	230		154
International And Structured Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		32		32
Loss and loss adjustment expense reserves	[1]	335		488
International And Structured Finance Insurance [Member] | Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		31		30
Loss and loss adjustment expense reserves	[1]	243		285
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		(1)		(2)
Loss and loss adjustment expense reserves	[1]	$ (92)		$ (203)

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