This element represents the gross amount of claim payments during the period

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- Definition

Debt instrument maturity year.

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No definition available.

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- Definition

Amount of outstanding bonds for a specific issuer

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No definition available.

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- Definition

Payment For Sale Of Subsidiary

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No definition available.

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- Definition

Par value of MBIA Inc. senior notes owned by National as of the balance sheet date.

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No definition available.

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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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No definition available.

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- Definition

This element represents disclosure of the aggregate cash dividends paid to the entity by consolidated subsidiaries.

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- Definition

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

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- Definition

Date the entity disposed of a business or a group of assets, in CCYY-MM-DD format.

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No definition available.

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- Definition

Amount of gain (loss) on sale or disposal of equity in securities of subsidiaries.

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- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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No definition available.

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- Definition

The cash inflow from a borrowing with the highest claim on the assets of the entity in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle, if longer).

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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.

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Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

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Business Developments And Risks And Uncertainties (Narrative) (Detail) $ in Millions		3 Months Ended		9 Months Ended
	Oct. 10, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) segments	Sep. 30, 2016 USD ($)	Nov. 01, 2017 USD ($)
Business Acquisition [Line Items]
Number of operating segments \| segments				3
Income (loss) before income taxes		$ (273)	$ 55	$ (603)	$ (101)
Proceeds from Senior Lenders				325
Valuation allowance taken in current period				1,200
Zohar II [Member]
Business Acquisition [Line Items]
Claims payments				770
Puerto Rico [Member]
Business Acquisition [Line Items]
Claims payments				242
Mbia Inc [Member]
Business Acquisition [Line Items]
Proceeds from subordinated financing				38
Mbia Corp [Member] \| Zohar II [Member]
Business Acquisition [Line Items]
Claims payments				60
National [Member] \| SubsequentEvent [Member]
Business Acquisition [Line Items]
Dividends from subsidiaries	$ 118
Assured Guaranty Corp [Member]
Business Acquisition [Line Items]
Payment for sale of subsidiary				23
Assured Guaranty Corp [Member] \| Zohar II [Member]
Business Acquisition [Line Items]
Outstanding bonds		$ 347		347
MBIA UK [Member]
Business Acquisition [Line Items]
Gain recorded on adjustment of carrying value to fair value less costs to sell				$ 5
Income (loss) before income taxes			$ 9		$ 32
Sale effective date				Jan. 10, 2017
MBIA Inc Senior Notes [Member]
Business Acquisition [Line Items]
Long-term debt, interest rate		5.70%		5.70%
Long-term debt, maturity year				2034
MBIA Inc Senior Notes [Member] \| National [Member] \| SubsequentEvent [Member]
Business Acquisition [Line Items]
Senior notes at par value owned by National						$ 130
MBIA Corp Surplus Notes [Member]
Business Acquisition [Line Items]
Long-term debt, interest rate		14.00%		14.00%