Loss And Loss Adjustment Expense Reserves (Schedule Of Financial Guarantees And Related Claim Liability) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015 policy issue		Dec. 31, 2014 issue policy
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	310		315
Number of issues	145	[1]	147	[1]
Remaining weighted average contract period (in years)	7 years 7 months 6 days		7 years 8 months 12 days
Principal	$ 10,884	[2]	$ 11,263	[2]
Interest	4,371	[2]	4,620	[2]
Total	15,255	[2]	15,883	[2]
Gross claim liability	791		850
Less: Gross potential recoveries	719		860
Discount, net	96	[3]	14	[3]
Net claim liability (recoverable)	(24)		(24)
Unearned premium revenue	158		167
Caution List Low [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	31		38
Number of issues	16	[1]	18	[1]
Remaining weighted average contract period (in years)	6 years 9 months 18 days		7 years 2 months 12 days
Principal	1,573	[2]	1,757	[2]
Interest	593	[2]	696	[2]
Total	2,166	[2]	2,453	[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	60		63
Caution List Medium [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	102		98
Number of issues	6	[1]	7	[1]
Remaining weighted average contract period (in years)	12 years 1 month 6 days		12 years 0 months 0 days
Principal	1,375	[2]	1,372	[2]
Interest	822	[2]	819	[2]
Total	2,197	[2]	2,191	[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	17		19
Caution List High [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	5		4
Number of issues	4	[1]	3	[1]
Remaining weighted average contract period (in years)	9 years 4 months 24 days		10 years 1 month 6 days
Principal	156	[2]	133	[2]
Interest	80	[2]	68	[2]
Total	236	[2]	201	[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		5
Classified List [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	172		175
Number of issues	119	[1]	119	[1]
Remaining weighted average contract period (in years)	6 years 10 months 24 days		7 years 0 months 0 days
Principal	7,780	[2]	8,001	[2]
Interest	2,876	[2]	3,037	[2]
Total	10,656	[2]	11,038	[2]
Gross claim liability	791		850
Less: Gross potential recoveries	719		860
Discount, net	96	[3]	14	[3]
Net claim liability (recoverable)	(24)		(24)
Unearned premium revenue	$ 76		$ 80

[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.