Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUES OF ASSETS AND LIABILITIES - Level 3 Roll Forward (Details)

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FAIR VALUES OF ASSETS AND LIABILITIES - Level 3 Roll Forward (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]            
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs $ 1 $ 3 $ 1 $ 3 $ (1) $ (2)
Available-for-sale securities 14,070   14,070   14,869  
Assets Level 3 Roll Forward:            
Transfers into Level 3     0 0    
Transfers out of Level 3 (1)     (14) (3)    
Total gains/losses for the period:            
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings     16 8    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Other Comprehensive Income (Loss)     0 0    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Purchases     0 0    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Sales     0 0    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Settlements     0 0    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Change in Unrealized Gain (Loss)     2 8    
MSRs            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]            
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3     0 0    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3     0 0    
Assets Level 3 Roll Forward:            
Opening balance 12 13 11 14    
Transfers into Level 3 0 0        
Transfers out of Level 3 (1) 0 0        
Total gains/losses for the period:            
Included in earnings (1) 0 0 (1)    
Included in OCI 0 0 0 0    
Purchases/originations 0 0 0 0    
Sales 0 0 0 0    
Repayments 0 0 0 0    
Settlements 0 0 0 0    
Closing balance 11 13 11 13    
Change in unrealized gains or losses for the period included in earnings for assets held at end of the reporting date (1) 0 0 (1)    
Derivative instruments            
Assets Level 3 Roll Forward:            
Opening balance 0 3        
Transfers into Level 3 0 0        
Transfers out of Level 3 (1) 9 2        
Total gains/losses for the period:            
Included in earnings 10 2        
Included in OCI 0 0        
Purchases/originations 0 0        
Sales 0 0        
Repayments 0 0 0 0    
Settlements 0 0        
Closing balance 1 3 1 3    
Change in unrealized gains or losses for the period included in earnings for assets held at end of the reporting date 2 3        
Municipal securities            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]            
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3     0 0    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3     0 0    
Assets Level 3 Roll Forward:            
Opening balance 3,230 2,868 3,167 2,798    
Transfers into Level 3 0 0        
Transfers out of Level 3 (1) 0 0        
Total gains/losses for the period:            
Included in earnings (1) (1) (2) (3)    
Included in OCI (9) 12 (37) 33    
Purchases/originations 86 115 279 248    
Sales 0 0 0 0    
Repayments 0 0 0 0    
Settlements (128) (122) (229) (204)    
Closing balance 3,178 2,872 3,178 2,872    
Change in unrealized gains or losses for the period included in earnings for assets held at end of the reporting date 0 12 0 33    
Asset-backed securities            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]            
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3     0 0    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3     0 0    
Assets Level 3 Roll Forward:            
Opening balance   59 24 76    
Transfers into Level 3   0        
Transfers out of Level 3 (1)   0        
Total gains/losses for the period:            
Included in earnings   (3) (2) (3)    
Included in OCI   6 11 9    
Purchases/originations   0 0 0    
Sales   (19) (33) (38)    
Repayments   0 0 0    
Settlements   0 0 (1)    
Closing balance 0 43 0 43    
Change in unrealized gains or losses for the period included in earnings for assets held at end of the reporting date   6 0 9    
Automobile            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]            
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3     0 0    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3     0 0    
Assets Level 3 Roll Forward:            
Opening balance 37 44 38 48    
Transfers into Level 3 0 0        
Transfers out of Level 3 (1) 0 0        
Total gains/losses for the period:            
Included in earnings 0 2 0 1    
Included in OCI 0 0 0 0    
Purchases/originations 0 0 0 0    
Sales 0 0 0 0    
Repayments (3) (2) (4) (5)    
Settlements 0 0 0 0    
Closing balance 34 44 34 44    
Change in unrealized gains or losses for the period included in earnings for assets held at end of the reporting date 0 $ 0 0 $ 0    
Commercial Mortgage Backed Securities [Member]            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]            
Available-for-sale securities 1,743   1,743   2,487  
Residential Mortgage Backed Securities [Member]            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]            
Available-for-sale securities 659   659   1,367  
Fair Value, Measurements, Recurring [Member]            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]            
Available-for-sale securities 14,070   14,070   14,869  
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage Backed Securities [Member]            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]            
Available-for-sale securities 1,743   1,743   2,487  
Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member]            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]            
Available-for-sale securities 659   659   1,367  
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]            
Available-for-sale securities 10,886   10,886   11,673  
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Mortgage Backed Securities [Member]            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]            
Available-for-sale securities 1,743   1,743   2,487  
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities [Member]            
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]            
Available-for-sale securities $ 659   $ 659   $ 1,367