Loss and Loss Adjustment Expense Reserves (Schedule of Losses and Loss Adjustment Expenses Reserves and Recoveries) (Detail) - USD ($) $ in Millions		Dec. 31, 2022		Dec. 31, 2021		Dec. 31, 2020
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves		$ 439	[1]	$ 894	[1]	$ 990
Insurance Loss Recoverable [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		137		1,296		$ 1,677
Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		137		1,296
Loss and loss adjustment expense reserves		439		894
US Public Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		107		1,054
Loss and loss adjustment expense reserves	[1]	154		425
International And Structured Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		32		244
Loss and loss adjustment expense reserves	[1]	488		687
International And Structured Finance Insurance [Member] | Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		30		242
Loss and loss adjustment expense reserves	[1]	285		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]	$ (203)		$ (218)

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