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Securities Available for Sale and Securities Held to Maturity - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2013
CreditScore
Mar. 31, 2012
Dec. 31, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]        
Securities available for sale Gross Unrealized Losses $ 52   $ 73  
Fair Isaac & Company minimum credit score for Prime loan origination 620      
Securities available for sale Amortized Cost 48,329   45,644  
Securities available for sale 48,809   46,123  
Cash and cash equivalents 6,931 6,794 12,663 8,679
Loan-to-deposit ratio 14.00%      
Net impairment losses on securities 4 [1] 18 [1]    
Proceeds from sale of available for sale securities   250    
Alt-A residential mortgage backed securities
       
Schedule of Available-for-sale Securities [Line Items]        
Securities available for sale Amortized Cost 295      
Securities available for sale $ 269      
[1] Net impairment losses on securities include total other-than-temporary impairment losses of $0 million and $2 million, net of $(4) million and $(16) million reclassified from other comprehensive income, for the three months ended March 31, 2013 and 2012, respectively.