Loan Receivables (Narrative) (Details) (USD $)
3 Months Ended
Mar. 31, 2015
segment
Mar. 31, 2014
Dec. 31, 2014
Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]        
Number of loan portfolio segments (in segments) 3      
Private student loan forbearance lifetime cap (in months) 12 months      
Private student loans including PCI in forbearance $ 54,000,000   $ 49,000,000  
Private student loans in forbearance as a percentage of student loans in repayment and forbearance (in percent) 0.90%   0.80%  
Percentage of defaulted loans that were charged off at the end of the month in which they defaulted (in percent) 43.00% 34.00%    
Provision for loan losses on PCI loans 390,000,000 272,000,000    
Allowance for loan losses on PCI loans 1,776,000,000 1,591,000,000 1,746,000,000 1,648,000,000
Private Student Loans [Member]        
Accounts, Notes, Loans and Financing Receivable [Line Items]        
Maximum period of payment reduction for the temporary reduced payment program (in months) 12 months      
Maximum forbearance period for student loan borrowers (in months) 12 months      
Period triggering TDR accounting for the temporary reduced payment program (in months) 12 months      
Personal Loans [Member]        
Accounts, Notes, Loans and Financing Receivable [Line Items]        
Maximum period of payment reduction for the temporary reduced payment program (in months) 12 months      
Maximum repayment term for temporary modification programs (in years) 9 years      
Maximum repayment term for permanent modification programs (in years) 9 years      
Purchased Credit-Impaired Loans [Member]        
Accounts, Notes, Loans and Financing Receivable [Line Items]        
Purchased credit-impaired loans outstanding balance 3,800,000,000   3,900,000,000  
Purchased credit-impaired loans 3,519,000,000 [1]   3,660,000,000 [1]  
Provision for loan losses on PCI loans 0 0    
Allowance for loan losses on PCI loans 28,000,000   28,000,000  
30 days or more delinquency rate on PCI student loans (in percent) 2.15%   2.35%  
90 days or more delinquency rate on PCI student loans (in percent) 0.70%   0.75%  
Net charge-off rate on PCI student loans (in percent) 0.50% 0.75%    
Credit Card Receivable [Member]        
Accounts, Notes, Loans and Financing Receivable [Line Items]        
Maximum period of payment reduction for the temporary reduced payment program (in months) 12 months      
Permanent workout program maturity (in months) 60 months      
Interest and fees forgiven due to credit card loan modification program 11,000,000 10,000,000    
Provision for loan losses on PCI loans 337,000,000 230,000,000    
Allowance for loan losses on PCI loans $ 1,492,000,000 $ 1,342,000,000 $ 1,474,000,000 $ 1,406,000,000
[1] Amounts include $1.9 billion and $2.0 billion of loans pledged as collateral against the notes issued from the Student Loan Corporation ("SLC") securitization trusts at March 31, 2015 and December 31, 2014, respectively. See Note 4: Credit Card and Student Loan Securitization Activities.