Annual report pursuant to Section 13 and 15(d)

LOAN SALES AND SECURITIZATIONS - Automobile Loans, MSRs Amortization Method (Details)

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LOAN SALES AND SECURITIZATIONS - Automobile Loans, MSRs Amortization Method (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Servicing Asset at Amortized Cost, Balance [Roll Forward]      
Fair value, end of year $ 238 $ 226  
Automobile      
Servicing Asset at Amortized Cost, Balance [Roll Forward]      
Carrying value, beginning of year 18 9  
New servicing assets created     $ 11
Amortization and other (10) (6)  
Carrying value, end of year 8 18 $ 9
Fair value, end of year $ 9 $ 18  
Automobile | Sensitivity Analysis Amortization Carrying Method      
Servicing Asset at Amortized Cost, Balance [Roll Forward]      
Weighted-average life (years) 3 years 6 months 4 years 2 months