Loss And Loss Adjustment Expense Reserves (Schedule Of Financial Guarantees And Related Claim Liability) (Detail) $ in Millions		12 Months Ended
		Dec. 31, 2017 USD ($) issue policy	Dec. 31, 2016 USD ($) issue policy
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		375	430
Number of issues | issue	[1]	144	149
Remaining weighted average contract period (in years)		8 years 10 months 24 days	7 years 1 month 6 days
Principal	[2]	$ 8,964	$ 10,285
Interest	[2]	8,481	5,683
Total	[2]	17,445	15,968
Gross claim liability	[3]	1,082	718
Less: Gross potential recoveries	[4]	782	770
Discount, net	[5]	(178)	(75)
Net claim liability (recoverable)		478	23
Unearned premium revenue		$ 90	$ 85
Caution List Low [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		89	90
Number of issues | issue	[1]	20	17
Remaining weighted average contract period (in years)		7 years 4 months 24 days	7 years 6 months
Principal	[2]	$ 2,764	$ 2,917
Interest	[2]	2,676	2,795
Total	[2]	5,440	5,712
Gross claim liability	[3]	0	0
Less: Gross potential recoveries		0	0
Discount, net	[5]	0	0
Net claim liability (recoverable)		0	0
Unearned premium revenue		$ 9	$ 9
Caution List Medium [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		5	6
Number of issues | issue	[1]	4	4
Remaining weighted average contract period (in years)		4 years 3 months 18 days	3 years 4 months 24 days
Principal	[2]	$ 13	$ 17
Interest	[2]	3	4
Total	[2]	16	21
Gross claim liability	[3]	0	0
Less: Gross potential recoveries		0	0
Discount, net	[5]	0	0
Net claim liability (recoverable)		0	0
Unearned premium revenue		$ 0	$ 0
Caution List High [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		1	3
Number of issues | issue	[1]	1	2
Remaining weighted average contract period (in years)		8 years 8 months 12 days	7 years 2 months 12 days
Principal	[2]	$ 104	$ 320
Interest	[2]	46	107
Total	[2]	150	427
Gross claim liability	[3]	0	0
Less: Gross potential recoveries		0	0
Discount, net	[5]	0	0
Net claim liability (recoverable)		0	0
Unearned premium revenue		$ 4	$ 8
Classified List [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		280	331
Number of issues | issue	[1]	119	126
Remaining weighted average contract period (in years)		9 years 8 months 12 days	7 years
Principal	[2]	$ 6,083	$ 7,031
Interest	[2]	5,756	2,777
Total	[2]	11,839	9,808
Gross claim liability	[3]	1,082	718
Less: Gross potential recoveries	[4]	782	770
Discount, net	[5]	(178)	(75)
Net claim liability (recoverable)		478	23
Unearned premium revenue		$ 77	$ 68

[1] An “issue” represents the aggregate of financial guarantee policies that share the same revenue source for purposes of making debt service payments on the insured debt.

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

[3] The gross claim liability with respect to Puerto Rico and Zohar II exposures are net of expected recoveries for policies in a net payable position.

[4] Gross potential recoveries with respect to certain Puerto Rico exposures are net of the claim liability for policies in a net recoverable position.

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