Consolidated Statements Of Comprehensive Income (Loss) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Net income (loss)	$ 164	$ 10
Unrealized gains (losses) on available-for-sale securities:
Unrealized gains (losses) arising during the period	13	47
Provision (benefit) for income taxes	4	6
Total	9	41
Reclassification adjustments for (gains) losses included in net income (loss)	(25)	135
Provision (benefit) for income taxes	(9)	47
Total	(16)	88
Other-than-temporary impairments on available-for-sale securities:
Other-than-temporary impairments arising during the period	5	11
Provision (benefit) for income taxes	2	4
Total	3	7
Reclassification adjustments for (gains) losses included in net income (loss)		41
Provision (benefit) for income taxes		15
Total		26
Net foreign currency translation gains (losses)	(43)	(12)
Accumulated Other Comprehensive Income, Net current period other comprehensive income	(47)	150
Comprehensive income (loss)	$ 117	$ 160

Name:	mbi_UnrealizedGainsAndLossesRelatedToAvailableForSaleSecuritiesAbstract
Namespace Prefix:	mbi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The change in equity [net assets] of a business enterprise during a period from transactions and other events and circumstances from non-owner sources which are attributable to the reporting entity. It includes all changes in equity during a period except those resulting from investments by owners and distributions to owners, but excludes any and all transactions which are directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent.