Investment Income And Gains and Losses (Total Investment Income From all Operations) (Details) (USD $) In Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Gross investment income	$ 111		$ 120		$ 243		$ 259
Investment expenses							2
Net investment income	111		120		243		257
Total net realized gains (losses)	(19)	[1]	(14)	[1]	4	[1]	(44)	[1]
Total investment income	92		106		247		213
Realized gains on trading securities					3.0
Fixed-Maturity Investments [Member]
Gross investment income	87		98		194		211
Gains	18	[2]	6		72	[2]	35
Losses	(37)		(20)		(77)		(78)
Total net realized gains (losses)	(19)		(14)		(5)		(43)
Held-To-Maturity [Member]
Gross investment income	1		2		3		4
Other Investments: [Member]
Gross investment income	3		6		8		11
Gains					9
Losses							(1)
Total net realized gains (losses)					9		(1)
Variable Interest Entity, Primary Beneficiary [Member]
Gross investment income	16		13		34		28
Short-Term Investments [Member]
Gross investment income	$ 4		$ 1		$ 4		$ 5

[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.

[2] Includes net trading gains of $3 million.