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Variable Interest Entities (Narrative) (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Variable Interest Entity [Line Items]      
Carrying amounts of assets $ 21,724 $ 26,873 $ 32,279
Carrying amounts of liabilities 18,530 25,150  
Additional VIEs were consolidated during 0    
Net realized gains related to deconsolidation   271  
Variable Interest Entity [Member]
     
Variable Interest Entity [Line Items]      
Carrying amounts of assets 8,300 10,900  
Carrying amounts of liabilities 7,300 9,900  
Net realized gains related to deconsolidation 0    
Net realized gain (losses) related to the initial consolidation   $ 16 $ 76