Loss And Loss Adjustment Expense Reserves (Schedule Of Financial Guarantees And Related Claim Liability) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2012 Policies Issues		Dec. 31, 2011 Issues Policies
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	295		296
Number of issues	189	[1]	191	[1]
Remaining weighted average contract period (in years)	8 years 9 months 18 days		8 years 9 months 18 days
Principal	$ 15,312	[2]	$ 16,504	[2]
Interest	8,696	[2]	8,984	[2]
Total	24,008	[2]	25,488	[2]
Gross claim liability	1,686		1,812
Less: Gross potential recoveries	3,879		3,813
Discount, net	166		177
Net claim liability (recoverable)	(2,359)		(2,178)
Unearned premium revenue	279		308
Caution List Low [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	53		54
Number of issues	29	[1]	32	[1]
Remaining weighted average contract period (in years)	8 years 9 months 18 days		8 years 2 months 12 days
Principal	3,652	[2]	4,310	[2]
Interest	2,670	[2]	2,653	[2]
Total	6,322	[2]	6,963	[2]
Unearned premium revenue	132		155
Caution List Medium [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	27		28
Number of issues	16	[1]	18	[1]
Remaining weighted average contract period (in years)	4 years 9 months 18 days		5 years 7 months 6 days
Principal	1,408	[2]	1,213	[2]
Interest	358	[2]	351	[2]
Total	1,766	[2]	1,564	[2]
Unearned premium revenue	17		16
Caution List High [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	11		14
Number of issues	10	[1]	11	[1]
Remaining weighted average contract period (in years)	7 years 4 months 24 days		6 years
Principal	395	[2]	561	[2]
Interest	121	[2]	144	[2]
Total	516	[2]	705	[2]
Unearned premium revenue	4		3
Classified List [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	204		200
Number of issues	134	[1]	130	[1]
Remaining weighted average contract period (in years)	9 years 6 months		9 years 7 months 6 days
Principal	9,857	[2]	10,420	[2]
Interest	5,547	[2]	5,836	[2]
Total	15,404	[2]	16,256	[2]
Gross claim liability	1,686		1,812
Less: Gross potential recoveries	3,879		3,813
Discount, net	166		177
Net claim liability (recoverable)	(2,359)		(2,178)
Unearned premium revenue	$ 126		$ 134

[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.