Loss and Loss Adjustment Expense Reserves (Schedule of Losses and Loss Adjustment Expenses Reserves and Recoveries) (Detail) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves	[1]	$ 470	$ 473
Insurance Loss Recoverable [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		179	183
Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		179	183
Loss and loss adjustment expense reserves		470	473
US Public Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		150	152
Loss and loss adjustment expense reserves	[1]	234	230
International And Structured Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		30	32
Loss and loss adjustment expense reserves	[1]	321	335
International And Structured Finance Insurance [Member] | Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		29	31
Loss and loss adjustment expense reserves	[1]	236	243
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)	(1)
Loss and loss adjustment expense reserves	[1]	$ (85)	$ (92)

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