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 VIEs) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Loss And Loss Adjustment Expense Reserves [Line Items]
Outstanding, Gross Principal	$ 16,504	[1]	$ 19,096	[1]
Outstanding, Gross Interest	8,984	[1]	10,853	[1]
Gross Undiscounted, Claim Liability	1,812		2,692
Gross Undiscounted, Potential Recoveries	3,813		4,045
Insured Issues Designated As Classified List [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Issues	34
Outstanding, Gross Principal	7,500
Outstanding, Gross Interest	2,800
Gross Undiscounted, Claim Liability	600
Gross Undiscounted, Potential Recoveries	4,600
Loan Files Reviewed With Potential Recoveries [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Issues	26
Outstanding, Gross Principal	7,100
Outstanding, Gross Interest	2,700
Gross Undiscounted, Claim Liability	600
Gross Undiscounted, Potential Recoveries	$ 4,500

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