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, 2023 USD ($) issue policy	Dec. 31, 2022 USD ($) issue policy
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		142	161
Number of issues | issue	[1]	95	99
Remaining weighted average contract period (in years)		6 years 4 months 24 days	6 years 4 months 24 days
Principal	[2]	$ 2,939	$ 3,185
Interest	[2]	2,323	2,508
Total	[2]	5,262	5,693
Gross claim liability	[3]	591	677
Less: Gross potential recoveries	[4]	152	198
Discount, net	[5]	156	179
Net claim liability (recoverable)		283	300
Unearned premium revenue		19	20
Reinsurance recoverable on paid and unpaid losses	[6]	$ 3	$ 10
Caution List Low [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies | policy		41	57
Number of issues | issue	[1]	15	17
Remaining weighted average contract period (in years)		5 years 9 months 18 days	5 years 8 months 12 days
Principal	[2]	$ 1,496	$ 1,723
Interest	[2]	1,751	1,905
Total	[2]	3,247	3,628
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		$ 10	$ 11
Caution List Medium [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)		9 months 18 days	2 years 4 months 24 days
Principal	[2]	$ 2	$ 4
Interest	[2]	0	1
Total	[2]	2	5
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		100	101
Number of issues | issue	[1]	79	80
Remaining weighted average contract period (in years)		7 years	7 years 2 months 12 days
Principal	[2]	$ 1,441	$ 1,458
Interest	[2]	572	602
Total	[2]	2,013	2,060
Gross claim liability	[3]	591	677
Less: Gross potential recoveries	[4]	152	198
Discount, net	[5]	156	179
Net claim liability (recoverable)		283	300
Unearned premium revenue		$ 9	$ 9

[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.