Loss And Loss Adjustment Expense Reserves (Schedule Of Financial Guarantees And Related Claim Liability) (Detail) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2020 USD ($) issue policy	Dec. 31, 2019 USD ($) issue policy
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		279	276
Number of issues | issue	[1]	116	112
Remaining weighted average contract period (in years)		7 years 4 months 24 days	7 years 8 months 12 days
Principal	[2]	$ 5,152	$ 5,588
Interest	[2]	3,579	3,885
Total	[2]	8,731	9,473
Gross claim liability	[3]	1,068	965
Less: Gross potential recoveries	[4]	1,781	2,184
Discount, net	[5]	(91)	(453)
Net claim liability (recoverable)		(622)	(766)
Unearned premium revenue		47	48
Reinsurance recoverables on paid and unpaid losses	[6]	$ 13	$ 19
Caution List Low [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		42	45
Number of issues | issue	[1]	12	13
Remaining weighted average contract period (in years)		6 years 7 months 6 days	7 years 3 months 18 days
Principal	[2]	$ 1,192	$ 1,546
Interest	[2]	1,914	2,107
Total	[2]	3,106	3,653
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	$ 6
Caution List Medium [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		18	19
Number of issues | issue	[1]	5	5
Remaining weighted average contract period (in years)		7 years 1 month 6 days	7 years 2 months 12 days
Principal	[2]	$ 224	$ 248
Interest	[2]	99	110
Total	[2]	323	358
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	$ 3
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		219	212
Number of issues | issue	[1]	99	94
Remaining weighted average contract period (in years)		7 years 8 months 12 days	7 years 10 months 24 days
Principal	[2]	$ 3,736	$ 3,794
Interest	[2]	1,566	1,668
Total	[2]	5,302	5,462
Gross claim liability	[3]	1,068	965
Less: Gross potential recoveries	[4]	1,781	2,184
Discount, net	[5]	(91)	(453)
Net claim liability (recoverable)		(622)	(766)
Unearned premium revenue		$ 38	$ 39

[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.