Loss And Loss Adjustment Expense Reserves (Schedule Of Financial Guarantees And Related Claim Liability) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 policy issue		Dec. 31, 2013 issue policy
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	315		299
Number of issues	147	[1]	180	[1]
Remaining weighted average contract period (in years)	7 years 8 months 12 days		9 years 8 months 12 days
Principal	$ 11,263	[2]	$ 14,264	[2]
Interest	4,620	[2]	8,632	[2]
Total	15,883	[2]	22,896	[2]
Gross claim liability	850		1,235
Less: Gross potential recoveries	860		1,085
Discount, net	14	[3]	205	[3]
Net claim liability (recoverable)	(24)		(55)
Unearned premium revenue	167		227
Caution List Low [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	38		83
Number of issues	18	[1]	26	[1]
Remaining weighted average contract period (in years)	7 years 2 months 12 days		11 years 0 months 0 days
Principal	1,757	[2]	5,290	[2]
Interest	696	[2]	3,829	[2]
Total	2,453	[2]	9,119	[2]
Gross claim liability	0		0
Less: Gross potential recoveries	0		0
Discount, net	0	[3]	0	[3]
Net claim liability (recoverable)	0		0
Unearned premium revenue	63		112
Caution List Medium [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	98		19
Number of issues	7	[1]	14	[1]
Remaining weighted average contract period (in years)	12 years 0 months 0 days		4 years 10 months 24 days
Principal	1,372	[2]	1,073	[2]
Interest	819	[2]	253	[2]
Total	2,191	[2]	1,326	[2]
Gross claim liability	0		0
Less: Gross potential recoveries	0		0
Discount, net	0	[3]	0	[3]
Net claim liability (recoverable)	0		0
Unearned premium revenue	19		19
Caution List High [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	4		5
Number of issues	3	[1]	4	[1]
Remaining weighted average contract period (in years)	10 years 1 month 6 days		11 years 6 months 0 days
Principal	133	[2]	40	[2]
Interest	68	[2]	24	[2]
Total	201	[2]	64	[2]
Gross claim liability	0		0
Less: Gross potential recoveries	0		0
Discount, net	0	[3]	0	[3]
Net claim liability (recoverable)	0		0
Unearned premium revenue	5		0
Classified List [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	175		192
Number of issues	119	[1]	136	[1]
Remaining weighted average contract period (in years)	7 years 0 months 0 days		9 years 6 months 0 days
Principal	8,001	[2]	7,861	[2]
Interest	3,037	[2]	4,526	[2]
Total	11,038	[2]	12,387	[2]
Gross claim liability	850		1,235
Less: Gross potential recoveries	860		1,085
Discount, net	14	[3]	205	[3]
Net claim liability (recoverable)	(24)		(55)
Unearned premium revenue	$ 80		$ 96

[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.

[3] Represents discount related to Gross Claim Liability and Gross Potential Recoveries.