Quarterly report pursuant to Section 13 or 15(d)

DERIVATIVE FINANCIAL INSTRUMENTS - Fair Value Hedges (Details)

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DERIVATIVE FINANCIAL INSTRUMENTS - Fair Value Hedges (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value hedging adjustments $ 84   $ 93
Fair Value Hedge Liabilities 7,775 $ 7,578 7,578
Hedged Liability, Fair Value Hedge, Cumulative Increase (Decrease) 304 114 $ 114
Interest expense subordinated notes and other long term debt [Member] | Subordinated notes [Member]      
Derivative Instruments, Gain (Loss) [Line Items]      
Increase (Decrease) in Fair Value of Hedged Item in Interest Rate Fair Value Hedge 200 41  
Interest expense subordinated notes and other long term debt [Member] | Hedged Subordinated notes [Member]      
Derivative Instruments, Gain (Loss) [Line Items]      
Increase (Decrease) in Fair Value of Hedged Item in Interest Rate Fair Value Hedge $ (190) $ (41)