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) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2011		Dec. 31, 2010
Loss And Loss Adjustment Expense Reserves [Line Items]
Outstanding, Gross Principal	$ 16,998	[1]	$ 19,096	[1]
Outstanding, Gross Interest	8,725	[1]	10,853	[1]
Gross Undiscounted, Claim Liability	1,988		2,692
Gross Undiscounted, Potential Recoveries	3,632		4,045
Insured Issues Designated As Classified List [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Issues	34
Outstanding, Gross Principal	7,900
Outstanding, Gross Interest	3,100
Gross Undiscounted, Claim Liability	700
Gross Undiscounted, Potential Recoveries	4,200
Loan Files Reviewed With Potential Recoveries [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Issues	27
Outstanding, Gross Principal	7,500
Outstanding, Gross Interest	3,000
Gross Undiscounted, Claim Liability	700
Gross Undiscounted, Potential Recoveries	$ 4,200

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