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v2.4.1.9

Income Taxes (Income Tax Rate Reconciliation) (Detail) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Effective income tax rate continuing operations tax rate reconciliation [Abstract] |  |  |
Federal income tax computed at the statutory rate | 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate | 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate | 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Increase (reduction) in taxes resulting from: [Abstract] |  |  |
Tax-exempt interest | (0.50%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome | (1.10%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome | (0.70%)us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome
Mark-to-market on warrants | (1.60%)mbi_EffectiveIncomeTaxRateReconciliationMarkToMarketOnWarrants | 3.80%mbi_EffectiveIncomeTaxRateReconciliationMarkToMarketOnWarrants | (0.70%)mbi_EffectiveIncomeTaxRateReconciliationMarkToMarketOnWarrants
Change in valuation allowance | (13.50%)us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance | (12.60%)us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance | (5.60%)us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance
Change in uncertain tax positions | (9.10%)mbi_EffectiveIncomeTaxrateReconciliationUncertainTaxPositions | 2.80%mbi_EffectiveIncomeTaxrateReconciliationUncertainTaxPositions | (0.10%)mbi_EffectiveIncomeTaxrateReconciliationUncertainTaxPositions
State income tax, net of federal benefit | 0.50%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes | 2.00%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes | 0.10%us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes
Out-of-period adjustment | 0.00%us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes | 0.00%us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes | (3.80%)us-gaap_EffectiveIncomeTaxRateReconciliationPriorYearIncomeTaxes
Foreign taxes | (0.50%)us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential | (0.80%)us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential | (1.20%)us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential
Basis difference in foreign subsidiary | 0.00%us-gaap_EffectiveIncomeTaxRateReconciliationRepatriationOfForeignEarnings | 11.40%us-gaap_EffectiveIncomeTaxRateReconciliationRepatriationOfForeignEarnings | 0.00%us-gaap_EffectiveIncomeTaxRateReconciliationRepatriationOfForeignEarnings
Other | 0.90%us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments | (0.60%)us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments | (0.20%)us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments
Effective tax rate | 11.20%us-gaap_EffectiveIncomeTaxRateContinuingOperations | 39.90%us-gaap_EffectiveIncomeTaxRateContinuingOperations | 22.80%us-gaap_EffectiveIncomeTaxRateContinuingOperations

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- Definition Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)(2)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Subparagraph 2 -Article 4 + Details
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- Definition Percentage of domestic federal statutory tax rate applicable to pretax income (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 + Details
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- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 + Details
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- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 + Details
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- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other adjustments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 + Details
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- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to revisions of previously reported income tax expense. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 + Details
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- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to the repatriation of foreign earnings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 + Details
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