Annual report pursuant to Section 13 and 15(d)

FAIR VALUES OF ASSETS AND LIABILITIES - Fair Value Option (Details)

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FAIR VALUES OF ASSETS AND LIABILITIES - Fair Value Option (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Fair Value, Option, Quantitative Disclosures [Line Items]    
Automobile loans, fair value $ 79 $ 93
Loans held for sale 613 413
Fair Value, Measurements, Recurring [Member]    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Loans held for sale 613 413
Fair Value, Measurements, Recurring [Member] | Mortgages Held For Sale [Member]    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Loans held for sale, aggregate unpaid principle 594 400
Aggregate difference (19) (13)
Fair Value, Measurements, Recurring [Member] | Mortgages Held To Maturity [Member]    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Loans held for investment, aggregate unpaid principle 87 102
Automobile loans, fair value 79 93
Aggregate difference (8) (9)
Fair Value, Measurements, Recurring [Member] | 90 or more days | Mortgages Held For Sale [Member]    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Loans held for sale, aggregate unpaid principle 0 1
Aggregate difference 0 0
Loans held for sale 0 1
Fair Value, Measurements, Recurring [Member] | 90 or more days | Mortgages Held To Maturity [Member]    
Fair Value, Option, Quantitative Disclosures [Line Items]    
Loans held for investment, aggregate unpaid principle 7 11
Automobile loans, fair value 6 10
Aggregate difference $ (1) $ (1)