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Commitments, Contingencies and Guarantees - Additional Information (Detail) (USD $)
Sep. 29, 2014
Commitments and Contingencies Disclosure [Abstract]  
FDIC civil monetary penalties $ 3,300,000slm_FDICcivilmonetarypenalties
Maximum [Member]  
Loss Contingencies [Line Items]  
Contingency refund $ 30,000,000slm_Contingencyrefund
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