Loss And Loss Adjustment Expense Reserves (Schedule Of Financial Guarantees And Related Claim Liability) (Detail) $ in Millions		9 Months Ended		12 Months Ended
		Sep. 30, 2017 USD ($) issue policy		Dec. 31, 2016 USD ($) issue policy
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		383		430
Number of issues | issue	[1]	145		149
Remaining weighted average contract period (in years)		8 years 9 months 18 days		7 years 1 month 6 days
Principal	[2]	$ 9,355		$ 10,285
Interest	[2]	8,620		5,683
Total	[2]	17,975		15,968
Gross claim liability	[3]	934		718
Less: Gross potential recoveries		934	[4]	770
Discount, net	[5]	(215)		(75)
Net claim liability (recoverable)		215		23
Unearned premium revenue		$ 93		$ 85
Caution List Low [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		93		90
Number of issues | issue	[1]	20		17
Remaining weighted average contract period (in years)		7 years 1 month 6 days		7 years 6 months
Principal	[2]	$ 3,016		$ 2,917
Interest	[2]	2,772		2,795
Total	[2]	5,788		5,712
Gross claim liability	[3]			0
Less: Gross potential recoveries				0
Discount, net	[5]			0
Net claim liability (recoverable)				0
Unearned premium revenue		$ 10		$ 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 7 months 6 days		3 years 4 months 24 days
Principal	[2]	$ 13		$ 17
Interest	[2]	4		4
Total	[2]	17		21
Gross claim liability	[3]			0
Less: Gross potential recoveries				0
Discount, net	[5]			0
Net claim liability (recoverable)				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 7 months 6 days		7 years 2 months 12 days
Principal	[2]	$ 108		$ 320
Interest	[2]	49		107
Total	[2]	157		427
Gross claim liability	[3]			0
Less: Gross potential recoveries				0
Discount, net	[5]			0
Net claim liability (recoverable)				0
Unearned premium revenue		$ 4		$ 8
Classified List [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		284		331
Number of issues | issue	[1]	120		126
Remaining weighted average contract period (in years)		9 years 8 months 12 days		7 years
Principal	[2]	$ 6,218		$ 7,031
Interest	[2]	5,795		2,777
Total	[2]	12,013		9,808
Gross claim liability	[3]	934		718
Less: Gross potential recoveries		934	[4]	770
Discount, net	[5]	(215)		(75)
Net claim liability (recoverable)		215		23
Unearned premium revenue		$ 79		$ 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 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.