Annual report pursuant to Section 13 and 15(d)

FAIR VALUES OF ASSETS AND LIABILITIES - Level 3 Classification of Gains/Losses (Details)

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FAIR VALUES OF ASSETS AND LIABILITIES - Level 3 Classification of Gains/Losses (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Net derivatives gain (loss) included in earnings $ 16 $ (1) $ 5
MSRs      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings (3) (4) (5)
Municipal securities      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings (2) 7 0
Private-label CMO      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings     0
Asset-backed securities      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings (5) (2) (3)
Automobile      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings 1 (2) 0
Mortgage banking income      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Net derivatives gain (loss) included in earnings 16 (1) 5
Mortgage banking income | MSRs      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings (3) (4) (5)
Mortgage banking income | Municipal securities      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings 0 0 0
Mortgage banking income | Asset-backed securities      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings 0 0 0
Mortgage banking income | Automobile      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings 0 0 0
Securities gains (losses)      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Net derivatives gain (loss) included in earnings 0 0 0
Securities gains (losses) | MSRs      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings 0 0 0
Securities gains (losses) | Municipal securities      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings 0 1 0
Securities gains (losses) | Asset-backed securities      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings (5) (2) (3)
Securities gains (losses) | Automobile      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings 0 0 0
Interest and fee income      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Net derivatives gain (loss) included in earnings 0 0 0
Interest and fee income | MSRs      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings 0 0 0
Interest and fee income | Municipal securities      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings (2) 0 0
Interest and fee income | Asset-backed securities      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings 0 0 0
Interest and fee income | Automobile      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings 0 0 0
Noninterest income      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Net derivatives gain (loss) included in earnings 0 0 0
Noninterest income | MSRs      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings 0 0 0
Noninterest income | Municipal securities      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings 0 6 0
Noninterest income | Asset-backed securities      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings 0 0 0
Noninterest income | Automobile      
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]      
Assets gain (loss) included in earnings $ 1 $ (2) $ 0