Loss And Loss Adjustment Expense Reserves (Schedule Of Losses And Loss Adjustment Expenses Reserves and Recoveries) (Detail) - USD ($) $ in Millions		Mar. 31, 2022	Dec. 31, 2021
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves	[1],[2]	$ 886	$ 894
Insurance Loss Recoverable [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		366	1,296
Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		366	1,296
Loss and loss adjustment expense reserves		886	894
US Public Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		128	1,054
Loss and loss adjustment expense reserves	[1]	460	425
International And Structured Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		240	244
Loss and loss adjustment expense reserves	[1]	635	687
International And Structured Finance Insurance [Member] | Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		238	242
Loss and loss adjustment expense reserves	[1]	426	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.