Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2009
Related Party Transactions [Abstract]
Voting interests of the Company	10.00%
Executed surety bonds to guarantee payment obligations	5
Outstanding exposure on surety bonds	$ 340
Invested in the MIPS Fund		25
Earned from investment in MIPS Fund		$ 0.2

Number of executed surety bonds to guarantee payment obligations.

No definition available.

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