Debt (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
MBIA Inc. Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument Interest Rate Stated Percentage	5.70%
Long-term debt, maturity year	2034
MBIA Corp Surplus Notes [Member]
Debt Instrument [Line Items]
Interest rate terms	Contractual interest rate is based on the three month LIBOR plus 11.26%. Callable on or after January 15, 2023 and every fifth anniversary thereafter at par.
Mbia Inc. Debentures [Member]
Debt Instrument [Line Items]
Debt Instrument Interest Rate Stated Percentage	7.00%
Long-term debt, maturity year	2025
Medium Term Notes [Member]
Debt Instrument [Line Items]
Repurchase of MTNs	$ 78
Weighted average interest rate	3.23%	2.90%
Percent of par	89.00%
Investment Agreement Obligations [Member]
Debt Instrument [Line Items]
Weighted average interest rate	5.83%	5.75%
MBIA Corp Financing Facility [Member]
Debt Instrument [Line Items]
Debt Instrument Interest Rate Stated Percentage	14.00%
Long-term debt, maturity date	Jan. 20, 2020
Commitment fees	$ 10
MBIA Corp Financing Facility [Member] \| Initial [Member]
Debt Instrument [Line Items]
Long-term debt principal amount owned	366
Proceeds from subordinated financing	38
MBIA Corp Financing Facility [Member] \| Undrawn [Member]
Debt Instrument [Line Items]
Proceeds from subordinated financing	50
MBIA Corp Financing Facility [Member] \| Outstanding [Member]
Debt Instrument [Line Items]
Long-term debt principal amount owned	373	$ 330
Mbia Inc [Member] \| MBIA Corp Surplus Notes [Member]
Debt Instrument [Line Items]
Long-term debt principal amount owned	13
National [Member] \| MBIA Inc. Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt principal amount purchased	44	$ 129
Long-term debt principal amount owned	308
National [Member] \| Mbia Inc. Debentures [Member]
Debt Instrument [Line Items]
Long-term debt principal amount purchased	10
Long-term debt principal amount owned	$ 10
Variable Interest Entity [Member]
Debt Instrument [Line Items]
Weighted average interest rate	6.91%	6.01%
Maximum [Member] \| Medium Term Notes [Member]
Debt Instrument [Line Items]
Debt Instrument Interest Rate Stated Percentage	6.00%	6.00%
Maximum [Member] \| Investment Agreement Obligations [Member]
Debt Instrument [Line Items]
Debt Instrument Interest Rate Stated Percentage	6.88%	6.88%
Maximum [Member] \| Variable Interest Entity [Member]
Debt Instrument [Line Items]
Debt Instrument Interest Rate Stated Percentage	14.00%	14.00%
Minimum [Member] \| Medium Term Notes [Member]
Debt Instrument [Line Items]
Debt Instrument Interest Rate Stated Percentage	0.00%	0.00%
Minimum [Member] \| Investment Agreement Obligations [Member]
Debt Instrument [Line Items]
Debt Instrument Interest Rate Stated Percentage	4.78%	4.74%
Minimum [Member] \| Variable Interest Entity [Member]
Debt Instrument [Line Items]
Debt Instrument Interest Rate Stated Percentage	2.81%	1.85%

Debt instrument maturity year.

No definition available.

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- Definition

Debt instruments repurchased weighted average percent of par value.

+ References

No definition available.

+ Details

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 944
-SubTopic 210
-Section S99
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Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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- Definition

Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets.

+ References

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- Definition

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.

+ References

No definition available.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
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- Definition

Fair value amount of debt instrument that was repurchased.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

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

+ References

No definition available.

+ Details

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- Definition

Represents the charge against earnings during the period for commitment fees and debt issuance expenses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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- Definition

The cash inflow from a borrowing where a lender is placed in a lien position behind debt having a higher priority of repayment (senior) in liquidation of the entity's assets or underlying collateral.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3255-108585

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