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
Mar. 31, 2020
Mar. 31, 2019
Mar. 31, 2020
Jan. 01, 2020
Dec. 31, 2019
Mar. 31, 2019
Dec. 31, 2018
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     $ 39   $ 6 $ 5 $ (2)
Assets Level 3 Roll Forward:              
Transfers into Level 3 $ 0            
Transfers out of Level 3 (1) (20) $ (9)          
Total gains/losses for the period:              
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings 53 12          
Included in OCI (68) 43          
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), Recurring Basis, Still Held, Unrealized Gain (Loss) 34 (2)          
MSRs              
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 0 0          
Assets Level 3 Roll Forward:              
Opening balance 7 10          
Total gains/losses for the period:              
Included in earnings (47) 0          
Included in OCI 0 0          
Purchases/originations 0 0          
Sales 0 0          
Repayments 0 0          
Settlements 0 0          
Closing balance 7 10 165 $ 205 7 10 10
Change in unrealized gains or losses for the period included in earnings for assets held at end of the reporting date (47) 0          
Derivative instruments              
Total gains/losses for the period:              
Repayments 0 0          
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            
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 0 0          
Assets Level 3 Roll Forward:              
Opening balance 2,999 3,165          
Total gains/losses for the period:              
Included in earnings (1) 1          
Included in OCI (68) (43)          
Purchases/originations 73 81          
Sales 0 0          
Repayments 0 0          
Settlements (66) (53)          
Closing balance 2,999 3,165 2,937   2,999 3,237 3,165
Change in unrealized gains or losses for the period included in earnings for assets held at end of the reporting date 0 0          
Mortgage-backed Securities, Issued by Private Enterprises [Member]              
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            
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 0            
Assets Level 3 Roll Forward:              
Opening balance 2            
Total gains/losses for the period:              
Included in earnings 0            
Included in OCI 0            
Purchases/originations 0            
Sales 0            
Repayments 0            
Settlements 0            
Closing balance 2   2   2    
Change in unrealized gains or losses for the period included in earnings for assets held at end of the reporting date 0            
Asset-backed Securities [Member]              
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            
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 0            
Assets Level 3 Roll Forward:              
Opening balance 48            
Total gains/losses for the period:              
Included in earnings 0            
Included in OCI 0            
Purchases/originations 27            
Sales 0            
Repayments 0            
Settlements (6)            
Closing balance 48   69   48    
Change in unrealized gains or losses for the period included in earnings for assets held at end of the reporting date 0            
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            
Real Estate Loan [Member]              
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 0 0          
Assets Level 3 Roll Forward:              
Opening balance 26 30          
Total gains/losses for the period:              
Included in earnings 0 0          
Included in OCI 0 0          
Purchases/originations 0 0          
Sales 0 0          
Repayments 0 (1)          
Settlements 0 0          
Closing balance 26 30 26   26 $ 29 $ 30
Change in unrealized gains or losses for the period included in earnings for assets held at end of the reporting date $ 0 $ 0          
Fair Value, Recurring [Member]              
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Available-for-sale securities     14,622   14,149    
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities [Member]              
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Available-for-sale securities     849   976    
Fair Value, Recurring [Member] | Residential Mortgage Backed Securities [Member]              
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Available-for-sale securities     4,304   4,222    
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]              
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Available-for-sale securities     11,606   11,090    
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities [Member]              
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Available-for-sale securities     849   976    
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Residential Mortgage Backed Securities [Member]              
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]              
Available-for-sale securities     $ 4,304   $ 4,222