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, 2024 USD ($) Issue Policy	Dec. 31, 2023 USD ($) Issue Policy
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | Policy		126	129
Number of issues | Issue	[1]	89	90
Remaining weighted average contract period (in years)		6 years 2 months 12 days	6 years 3 months 18 days
Principal	[2]	$ 2,481	$ 2,580
Interest	[2]	2,025	2,118
Total	[2]	4,506	4,698
Gross claim liability	[3]	852	651
Less: Gross potential recoveries	[4]	467	235
Discount, net	[5]	91	125
Net claim liability (recoverable)		294	291
Unearned premium revenue		15	16
Reinsurance recoverable on paid and unpaid losses	[6]	$ 13	$ 13
Caution List Low [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | Policy		30	35
Number of issues | Issue	[1]	11	13
Remaining weighted average contract period (in years)		5 years 10 months 24 days	5 years 7 months 6 days
Principal	[2]	$ 795	$ 1,336
Interest	[2]	1,396	1,614
Total	[2]	2,191	2,950
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		$ 5	$ 9
Caution List Medium [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
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		96	94
Number of issues | Issue	[1]	78	77
Remaining weighted average contract period (in years)		6 years 4 months 24 days	7 years 1 month 6 days
Principal	[2]	$ 1,686	$ 1,244
Interest	[2]	629	504
Total	[2]	2,315	1,748
Gross claim liability	[3]	852	651
Less: Gross potential recoveries	[4]	467	235
Discount, net	[5]	91	125
Net claim liability (recoverable)		294	291
Unearned premium revenue		$ 10	$ 7

[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.