Fair Value Of Financial Instruments (Changes In Fair Value Included In The Company's Consolidated Income Statement) (Details) (USD $) In Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	$ 13		$ 12		$ (114)		$ (36)
Realized Investment Gains Losses	(11)	[1]	50	[1]	(8)	[1]	6	[1]
Loan Repurchase Commitments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	33		2		103		296
Realized Investment Gains Losses							63
Total Changes in Fair Value	33		2		103		359
Fixed-Maturity Securities Held At Fair Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	(286)		90		(338)		337
Realized Investment Gains Losses							21
Total Changes in Fair Value	(286)		90		(338)		358
Other Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	(37)		38		(30)		56
Realized Investment Gains Losses
Total Changes in Fair Value	(37)		38		(30)		56
Residential Mortgage Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	(65)		(164)		65		204
Realized Investment Gains Losses							220
Total Changes in Fair Value	(65)		(164)		65		424
Other Assets [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	(162)		(1)		(184)		(3)
Realized Investment Gains Losses							159
Total Changes in Fair Value	(162)		(1)		(184)		156
Long-Term Debt [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	481		91		367		(332)
Realized Investment Gains Losses							(333)
Total Changes in Fair Value	$ 481		$ 91		$ 367		$ (665)

[1] Reported within 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.