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Debt (Narrative) (Detail) - USD ($) $ in Millions		12 Months Ended
	Jan. 20, 2017	Dec. 31, 2017	Dec. 31, 2016
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.
Medium Term Notes [Member]
Debt Instrument [Line Items]
Repurchase of MTNs		$ 160
Weighted average interest rate		2.90%	2.43%
Percent of par		84.00%
Investment Agreement Obligations [Member]
Debt Instrument [Line Items]
Weighted average interest rate		5.75%	5.66%
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	$ 366
Proceeds from subordinated financing	$ 38
MBIA Corp Financing Facility [Member] | Outstanding [Member]
Debt Instrument [Line Items]
Long-term debt		330
Mbia Inc [Member]
Debt Instrument [Line Items]
Proceeds from subordinated financing		38
Mbia Inc [Member] | MBIA Inc Senior Notes [Member]
Debt Instrument [Line Items]
Senior notes owned at par value		54
Mbia Inc [Member] | MBIA Corp Surplus Notes [Member]
Debt Instrument [Line Items]
Surplus notes owned at par value		13
National [Member] | MBIA Inc Senior Notes [Member]
Debt Instrument [Line Items]
Senior notes owned at par value		264
Senior notes purchased at par value		129
Mbia Corp [Member] | Undrawn [Member]
Debt Instrument [Line Items]
Proceeds from subordinated financing		$ 50
Variable Interest Entity [Member]
Debt Instrument [Line Items]
Weighted average interest rate		6.01%	2.25%
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%	6.89%
Maximum [Member] | Variable Interest Entity [Member]
Debt Instrument [Line Items]
Debt Instrument Interest Rate Stated Percentage		14.00%	2.77%
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		4.74%	4.48%
Minimum [Member] | Variable Interest Entity [Member]
Debt Instrument [Line Items]
Debt Instrument Interest Rate Stated Percentage		1.85%	1.07%

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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Contractual interest rate for funds borrowed, under the debt agreement.

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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.

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