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Commitments and Contingencies - Additional Information (Detail) - USD ($)
3 Months Ended 12 Months Ended
May 13, 2014
Mar. 31, 2017
Dec. 31, 2014
Dec. 31, 2013
Loss Contingencies [Line Items]        
Lawsuit Filing Date   May 4, 2015    
Lawsuit settlement date   January 26, 2017    
Total reserves established during year     $ 177,000,000 $ 177,000,000
Federal Deposit Insurance Corporation [Member]        
Loss Contingencies [Line Items]        
Establishment of a restitution reserve $ 30,000,000      
DOJ Order [Member]        
Loss Contingencies [Line Items]        
Settlement fund under DOJ     $ 60,000,000  
Consent order, term     4 years  
Navient Solutions LLC [Member] | Federal Deposit Insurance Corporation [Member]        
Loss Contingencies [Line Items]        
Civil monetary penalties $ 3,300,000      
Navient Solutions LLC [Member] | DOJ Order [Member]        
Loss Contingencies [Line Items]        
Civil monetary penalties     $ 55,000  
SLM BankCo [Member] | Indemnification Matters [Member]        
Loss Contingencies [Line Items]        
Reserve for estimated amounts and costs incurred   $ 0