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Allowance for Loan Losses - Recorded Investment, Unpaid Principal Balance and Related Allowance for TDR Loans (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2013
Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]    
TDR Loans, Recorded Investment $ 8,949 $ 7,294
TDR loans, unpaid principal balance 8,986 7,377
TDR Loans, Related Allowance 1,048 1,126
Private Education Loans - Traditional [Member]
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
TDR Loans, Recorded Investment 7,515 5,999
TDR loans, unpaid principal balance 7,559 6,074
TDR Loans, Related Allowance 812 844
Private Education Loans - Non-Traditional [Member]
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
TDR Loans, Recorded Investment 1,434 1,295
TDR loans, unpaid principal balance 1,427 1,303
TDR Loans, Related Allowance $ 236 $ 282