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Securities Available for Sale and Securities Held to Maturity - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
CreditScore
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Schedule of Available-for-sale Securities [Line Items]        
Securities available for sale Gross Unrealized Losses $ 73 $ 273    
Fair Isaac & Company minimum credit score for Prime loan origination 620      
Securities available for sale Amortized Cost 45,644 33,950    
Securities available for sale 46,123 33,965    
Cash and cash equivalents 12,663 8,679 4,931 8,241
Loan-to-deposit ratio 14.00%      
Net impairment losses on securities 32 [1] 31 [1] 36 [1]  
Alt-A residential mortgage backed securities
       
Schedule of Available-for-sale Securities [Line Items]        
Securities available for sale Amortized Cost 308      
Securities available for sale $ 269      
[1] Net impairment losses on securities include total other-than-temporary impairment losses of $15 million, $18 million, and $41 million, net of $(17) million, $(13) million, and $5 million recognized in other comprehensive income in 2012, 2011, and 2010, respectively.