Loss And Loss Adjustment Expense Reserves (Schedule Of Losses And Loss Adjustment Expenses Reserves and Recoveries) (Detail) - USD ($) $ in Millions		Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves	[2]	$ 894	[1]	$ 990	[1]	$ 901
Insurance Loss Recoverable [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		1,296		1,677		$ 1,694
Variable Interest Entity Primary Beneficiary [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loan repurchase commitments		0		604
Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		1,296		1,677
Loss and loss adjustment expense reserves		894		990
US Public Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		1,054		1,220
Loss and loss adjustment expense reserves	[1]	425		469
International And Structured Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable	[3]	244		1,082
Loss and loss adjustment expense reserves	[1],[3]	687		780
International And Structured Finance Insurance [Member] | Variable Interest Entity Primary Beneficiary [Member] | Loan Repurchase Commitments [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loan repurchase commitments				604
International And Structured Finance Insurance [Member] | Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable		242		457
Loss and loss adjustment expense reserves	[1]	469		521
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	[3]	(2)		(625)
Loss and loss adjustment expense reserves	[1],[3]	$ (218)		$ (259)

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

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

[3] Includes loan repurchase commitments of $604 million as of December 31, 2020.