Loss And Loss Adjustment Expense Reserves (Schedule Of Financial Guarantees And Related Claim Liability) (Detail) $ in Millions		6 Months Ended	12 Months Ended
		Jun. 30, 2017 USD ($) issue policy	Dec. 31, 2016 USD ($) issue policy
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		426	430
Number of issues | issue	[1]	147	149
Remaining weighted average contract period (in years)		8 years 9 months 18 days	7 years 1 month 6 days
Principal	[2]	$ 9,632	$ 10,285
Interest	[2]	8,791	5,683
Total	[2]	18,423	15,968
Gross claim liability	[3]	922	718
Less: Gross potential recoveries		823	770
Discount, net	[4]	(133)	(75)
Net claim liability (recoverable)		232	23
Unearned premium revenue		$ 96	$ 85
Caution List Low [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		95	90
Number of issues | issue	[1]	21	17
Remaining weighted average contract period (in years)		7 years 4 months 24 days	7 years 6 months
Principal	[2]	$ 3,005	$ 2,917
Interest	[2]	2,793	2,795
Total	[2]	5,798	5,712
Gross claim liability	[3]		0
Less: Gross potential recoveries			0
Discount, net	[4]		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 8 months 12 days	3 years 4 months 24 days
Principal	[2]	$ 14	$ 17
Interest	[2]	4	4
Total	[2]	18	21
Gross claim liability	[3]		0
Less: Gross potential recoveries			0
Discount, net	[4]		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 9 months 18 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	[4]		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		325	331
Number of issues | issue	[1]	121	126
Remaining weighted average contract period (in years)		9 years 6 months	7 years
Principal	[2]	$ 6,505	$ 7,031
Interest	[2]	5,945	2,777
Total	[2]	12,450	9,808
Gross claim liability	[3]	922	718
Less: Gross potential recoveries		823	770
Discount, net	[4]	(133)	(75)
Net claim liability (recoverable)		232	23
Unearned premium revenue		$ 82	$ 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.

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