Insurance Regulations And Dividends (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Insurance Regulations And Dividends [Line Items]
Percentage of policyholders' surplus	10.00%
Percentage of adjusted net investment income	100.00%
Maximum percentage of notional asset swap	5.00%
Minimum [Member]
Insurance Regulations And Dividends [Line Items]
Policyholders' surplus	$ 65
MBIA Corp [Member]
Insurance Regulations And Dividends [Line Items]
Statutory net loss	25	$ 35
Statutory capital	885	859
Policyholders' surplus	609
Contingency reserves	$ 276
MBIA Corp [Member] \| Minimum Surplus And Contingency Reserves [Member]
Insurance Regulations And Dividends [Line Items]
Investments in certain qualifing assets	100.00%
MBIA Corp [Member] \| Loss Reserves And Unearned Premium Reserves [Member]
Insurance Regulations And Dividends [Line Items]
Investments in certain qualifing assets	50.00%
MBIA Corp [Member] \| Policyholders Surplus [Member]
Insurance Regulations And Dividends [Line Items]
Statutory surplus negative impact	$ 75
Maximum percentage of statutory admitted assets invested in subsidiaries	60.00%
National [Member]
Insurance Regulations And Dividends [Line Items]
Dividends from subsidiaries	$ 114	220
Statutory capital	3,400	3,300
Policyholders' surplus	2,500
Contingency reserves	910
Statutory net income	$ 284	$ 238

Insurance Regulations And Dividends Line Items

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Percentage required to be invested in certain qualifing assets.

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Maximum percentage of admitted assets the asset swap can be without three month notice to initiate cash dividends.

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Maximum percentage of statutory admitted assets allowed to be invested in subsidaries under New York insurance laws.

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Percentage of adjusted net investment income.

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Percentage Of Policyholders Surplus

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Statutory Accounting Practices defined as policyholders' surplus plus contingency reserves.

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Statutory accounting practices, contingency reserves.

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Amount of net loss for the period determined using accounting principles prescribed or permitted by insurance regulators.

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Statutory accounting practices, surplus.

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Impact on statutory surplus due to maximum amount of investment in subsidiaries.

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(b))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 235
-Section S99
-Paragraph 2
-Subparagraph (SX 210.9-06)
-URI http://asc.fasb.org/extlink&oid=6882215&loc=d3e537971-122884

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-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph b
-Article 12

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-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 06
-Article 9

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Amount of net income for the period determined using accounting principles prescribed or permitted by insurance regulators.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.23(c))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 24
-Subparagraph c
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