Debt (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Aggregate unpaid contractual principal	$ 2,585	$ 2,428
Debt instrument principal amount repurchased	$ 308
Mbia Inc Debentures [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	7.00%
Long-term debt, maturity year	2025
Litigation Trust [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	18.00%
Long-term debt, maturity date	Aug. 02, 2027
Repayments of Debt		7
Litigation Trust [Member] \| Unfunded Loan Commitment [Member]
Debt Instrument [Line Items]
Other Commitment	$ 9
MBIA Inc. Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	5.70%
Long-term debt, maturity year	2034
MBIA Corp Surplus Notes [Member]
Debt Instrument [Line Items]
Callable date for fifth anniversary of initial callable date	Jan. 15, 2028
MBIA Corp Surplus Notes [Member] \| Mbia Inc Debentures [Member]
Debt Instrument [Line Items]
Debt instrument principal amount repurchased	$ 13
6.625% Debentures Due 2028 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	6.625%
Long-term debt, maturity year	2028
Aggregate unpaid contractual principal	$ 112	112
6.625% Debentures Due 2028 [Member] \| Mbia Inc Debentures [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	6.625%
Long-term debt, maturity year	2028
7.150% Debentures Due 2027 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	7.15%
Long-term debt, maturity year	2027
Aggregate unpaid contractual principal	$ 96	96
7.150% Debentures Due 2027 [Member] \| Mbia Inc Debentures [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	7.15%
Long-term debt, maturity year	2027
Third Party Loan [Member] \| Litigation Trust [Member]
Debt Instrument [Line Items]
Aggregate unpaid contractual principal	$ 3	2
7.000% Debentures Due 2025 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	7.00%
Long-term debt, maturity year	2025
Aggregate unpaid contractual principal	$ 45	$ 45
7.000% Debentures Due 2025 [Member] \| Mbia Inc Debentures [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	7.00%
Long-term debt, maturity year	2025
Medium-term notes [Member]
Debt Instrument [Line Items]
Weighted average interest rate	4.76%	4.65%
Medium-term notes [Member] \| Floating Rate [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	0.00%
Investment Agreement Obligations [Member]
Debt Instrument [Line Items]
Weighted average interest rate	6.06%	6.09%
Maximum [Member] \| Medium-term notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	5.90%	5.90%
Maximum [Member] \| Investment Agreement Obligations [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	6.88%	6.88%
Minimum [Member] \| Medium-term notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	2.21%	2.06%
Minimum [Member] \| Investment Agreement Obligations [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	4.78%	4.78%
MBIA Inc. [Member] \| MBIA Corp Surplus Notes [Member]
Debt Instrument [Line Items]
Long-term debt principal amount previously purchased	$ 13
National [Member] \| Mbia Inc Debentures [Member]
Debt Instrument [Line Items]
Debt instrument principal amount repurchased	10
Long-term debt principal amount previously purchased	308
National [Member] \| MBIA Inc. Senior Notes [Member] \| Mbia Inc Debentures [Member]
Debt Instrument [Line Items]
Debt instrument principal amount repurchased	10
Mbia Corp [Member]
Debt Instrument [Line Items]
Other Commitment	6
Mbia Corp [Member] \| 6.625% Debentures Due 2028 [Member]
Debt Instrument [Line Items]
Debt instrument principal amount repurchased		$ 24
Mbia Corp [Member] \| 6.625% Debentures Due 2028 [Member] \| Mbia Inc Debentures [Member]
Debt Instrument [Line Items]
Long-term debt principal amount previously purchased	29
Mbia Corp [Member] \| 7.150% Debentures Due 2027 [Member]
Debt Instrument [Line Items]
Debt instrument principal amount repurchased		4
Mbia Corp [Member] \| 7.150% Debentures Due 2027 [Member] \| Mbia Inc Debentures [Member]
Debt Instrument [Line Items]
Debt instrument principal amount repurchased	5
Mbia Corp [Member] \| 7.000% Debentures Due 2025 [Member]
Debt Instrument [Line Items]
Debt instrument principal amount repurchased		1
Mbia Corp [Member] \| 7.000% Debentures Due 2025 [Member] \| Mbia Inc Debentures [Member]
Debt Instrument [Line Items]
Debt instrument principal amount repurchased	1
Variable Interest Entity Primary Beneficiary [Member]
Debt Instrument [Line Items]
Aggregate unpaid contractual principal	328	780
MBIA Insured Variable Interest Entity Primary Beneficiary [Member]
Debt Instrument [Line Items]
Aggregate unpaid contractual principal	$ 96	$ 189

Debt instrument, call date for first fifth anniversary.

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- Definition

Debt instrument maturity year.

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- Definition

long-term debt principal amount previously purchased.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in YYYY-MM-DD format.

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- Definition

Face (par) amount of the original debt instrument that was repurchased.

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- Definition

Weighted average interest rate of debt outstanding.

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Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

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- Definition

Amount of cash outflow for short-term and long-term debt. Excludes payment of lease obligation.

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