Loss And Loss Adjustment Expense Reserves (Schedule Of Financial Guarantees And Related Claim Liability) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2011		Dec. 31, 2010
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	286		433
Number of issues	188	[1]	188	[1]
Remaining weighted average contract period (in years)	8.3		9.2
Gross insured contractual payments outstanding, Principal	$ 16,998	[2]	$ 19,096	[2]
Gross insured contractual payments outstanding, Interest	8,725	[2]	10,853	[2]
Gross insured contractual payments outstanding, Total	25,723	[2]	29,949	[2]
Gross claim liability	1,988		2,692
Gross potential recoveries	3,632		4,045
Discount, net	172		27
Net claim liability (recoverable)	(1,816)		(1,380)
Unearned premium revenue	313		377
Caution List Low [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	50		199
Number of issues	33	[1]	40	[1]
Remaining weighted average contract period (in years)	7.9		9.4
Gross insured contractual payments outstanding, Principal	4,728	[2]	5,041	[2]
Gross insured contractual payments outstanding, Interest	2,743	[2]	3,439	[2]
Gross insured contractual payments outstanding, Total	7,471	[2]	8,480	[2]
Unearned premium revenue	161		148
Caution List Medium [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	28		43
Number of issues	18	[1]	26	[1]
Remaining weighted average contract period (in years)	6.1		6.9
Gross insured contractual payments outstanding, Principal	974	[2]	1,419	[2]
Gross insured contractual payments outstanding, Interest	334	[2]	536	[2]
Gross insured contractual payments outstanding, Total	1,308	[2]	1,955	[2]
Unearned premium revenue	14		16
Caution List High [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	14		12
Number of issues	11	[1]	12	[1]
Remaining weighted average contract period (in years)	6.0		9.1
Gross insured contractual payments outstanding, Principal	543	[2]	1,446	[2]
Gross insured contractual payments outstanding, Interest	139	[2]	746	[2]
Gross insured contractual payments outstanding, Total	682	[2]	2,192	[2]
Unearned premium revenue	3		72
Classified List [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	194		179
Number of issues	126	[1]	110	[1]
Remaining weighted average contract period (in years)	8.8		9.4
Gross insured contractual payments outstanding, Principal	10,753	[2]	11,190	[2]
Gross insured contractual payments outstanding, Interest	5,509	[2]	6,132	[2]
Gross insured contractual payments outstanding, Total	16,262	[2]	17,322	[2]
Gross claim liability	1,988		2,692
Gross potential recoveries	3,632		4,045
Discount, net	172		27
Net claim liability (recoverable)	(1,816)		(1,380)
Unearned premium revenue	$ 135		$ 141

[1] An "issue" represents the aggregate of financial guarantee policies that share the same revenue source for purposes of making debt service payments

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