Investment Income And Gains And Losses (Total Investment Income From All Operations) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income	$ 77		$ 111		$ 156		$ 243
Total net realized gains (losses)	12	[1]	(19)	[1]	(119)	[1]	4	[1]
Total investment income	89		92		37		247
Fixed-Maturity Investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income	54		87		113		194
Gains	27		18		66		72
Losses	(19)		(37)		(176)		(77)
Total net realized gains (losses)	8		(19)		(110)		(5)
Held-To-Maturity [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income			1		1		3
Short-Term Investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income	3		4		3		4
Total Other Investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income	3		3		5		8
Gains	5				6		9
Losses	(1)				(15)
Total net realized gains (losses)	4				(9)		9
Variable Interest Entity [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income	$ 17		$ 16		$ 34		$ 34

[1] These balances are included in the "Net gains (losses) on financial instruments at fair value and foreign exchange" and "Net investment losses related to other-than-temporary impairments" line items on MBIA's consolidated statements of operations.