Related Party Transactions (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012 Bonds
Related Party Transactions Supervisory And Other Services [Line Items]
Voting interests of the company	10.00%
Executed surety bonds to guarantee payment obligations	5
Outstanding exposure on surety bonds	$ 340

Number of executed surety bonds to guarantee payment obligations.

No definition available.

Name:	mbi_NumberOfExecutedSuretyBondsToGuaranteePaymentObligations
Namespace Prefix:	mbi_
Data Type:	xbrli:positiveIntegerItemType
Balance Type:	na
Period Type:	duration