Loss And Loss Adjustment Expense Reserves (Schedule Of Financial Guarantees And Related Claim Liability) (Detail) $ in Millions		12 Months Ended
		Dec. 31, 2019 USD ($) issue policy	Dec. 31, 2018 USD ($) issue policy
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		276	301
Number of issues | issue	[1]	112	122
Remaining weighted average contract period (in years)		7 years 8 months 12 days	8 years 10 months 24 days
Principal	[2]	$ 5,588	$ 7,206
Interest	[2]	3,885	7,655
Total	[2]	9,473	14,861
Gross claim liability	[3]	965	1,085
Less: Gross potential recoveries	[4]	2,184	2,363
Discount, net	[5]	(453)	(670)
Net claim liability (recoverable)		(766)	(608)
Unearned premium revenue		48	72
Reinsurance recoverables on paid and unpaid losses	[6]	$ 19	$ 21
Caution List Low [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		45	50
Number of issues | issue	[1]	13	16
Remaining weighted average contract period (in years)		7 years 3 months 18 days	6 years 8 months 12 days
Principal	[2]	$ 1,546	$ 1,604
Interest	[2]	2,107	2,118
Total	[2]	3,653	3,722
Gross claim liability	[3]	0	0
Less: Gross potential recoveries	[4]	0	0
Discount, net	[5]	0	0
Net claim liability (recoverable)		0	0
Unearned premium revenue		$ 6	$ 5
Caution List Medium [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		19	18
Number of issues | issue	[1]	5	4
Remaining weighted average contract period (in years)		7 years 2 months 12 days	8 years
Principal	[2]	$ 248	$ 249
Interest	[2]	110	123
Total	[2]	358	372
Gross claim liability	[3]	0	0
Less: Gross potential recoveries	[4]	0	0
Discount, net	[5]	0	0
Net claim liability (recoverable)		0	0
Unearned premium revenue		$ 3	$ 4
Caution List High [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		0	0
Number of issues | issue	[1]	0	0
Principal	[2]	$ 0	$ 0
Interest	[2]	0	0
Total	[2]	0	0
Gross claim liability	[3]	0	0
Less: Gross potential recoveries	[4]	0	0
Discount, net	[5]	0	0
Net claim liability (recoverable)		0	0
Unearned premium revenue		$ 0	$ 0
Classified List [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		212	233
Number of issues | issue	[1]	94	102
Remaining weighted average contract period (in years)		7 years 10 months 24 days	9 years 8 months 12 days
Principal	[2]	$ 3,794	$ 5,353
Interest	[2]	1,668	5,414
Total	[2]	5,462	10,767
Gross claim liability	[3]	965	1,085
Less: Gross potential recoveries	[4]	2,184	2,363
Discount, net	[5]	(453)	(670)
Net claim liability (recoverable)		(766)	(608)
Unearned premium revenue		$ 39	$ 63

[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.

[6] Included in “Other assets” on the Company’s consolidated balance sheets.