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Investment Income And Gains And Losses (Total Investment Income From All Operations) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]    
Net investment income $ 79 $ 131
Total net realized gains (losses) (131) [1] 23 [1]
Total investment income (52) 154
Net trading gains on securities 4  
Fixed-Maturity Investments [Member]
    
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]    
Net investment income 58 107
Gains 39 [2] 54 [2]
Losses (157) (40)
Total net realized gains (losses) (118) 14
Held-To-Maturity [Member]
    
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]    
Net investment income 1 2
Short-Term Investments [Member]
    
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]    
Net investment income 1  
Total Other Investments [Member]
    
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]    
Net investment income 2 5
Gains 1 9
Losses (14)  
Total net realized gains (losses) (13) 9
Variable Interest Entity [Member]
    
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]    
Net investment income $ 17 $ 17
[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 $4 million for the three months ended March 31, 2012.