Loss And Loss Adjustment Expense Reserves (Schedule Of Company's Second-Lien RMBS Exposure, Gross Undiscounted Claim Liability And Potential Recoveries, Before The Elimination Of Amounts Related To Consolidated VIE's) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Loss And Loss Adjustment Expense Reserves [Line Items]
Outstanding Gross Principal	$ 15,312	[1]	$ 16,504	[1]
Gross Interest	8,696	[1]	8,984	[1]
Gross Undiscounted Claim Liability	1,686		1,812
Potential Recoveries	3,879		3,813
Insured Issues Designated As "Classified List" [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Issues	34
Outstanding Gross Principal	6,800
Gross Interest	2,600
Gross Undiscounted Claim Liability	400
Potential Recoveries	4,600
Loan Files Reviewed With Potential Recoveries [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Issues	26
Outstanding Gross Principal	6,400
Gross Interest	2,400
Gross Undiscounted Claim Liability	400
Potential Recoveries	$ 4,500

[1] Represents contractual principal and interest payments due by the issuer of the obligations insured by MBIA.