DERIVATIVES - Schedule of Derivative Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Derivative Assets
Derivative assets	$ 2,286	$ 984
Less: Gross amounts offset in the Consolidated Balance Sheets	(187)	(107)
Less: Cash collateral applied	(69)	(70)
Total net derivative fair values presented in the Consolidated Balance Sheets	2,030	807
Derivative Liabilities
Derivative Liabilities	506	322
Less: Gross amounts offset in the Consolidated Balance Sheets	(187)	(107)
Less: Cash collateral applied	(219)	(95)
Total net derivative fair values presented in the Consolidated Balance Sheets	100	120
Derivatives not designated as hedging instruments:
Derivative Assets
Derivative assets	2,282	983
Derivative Liabilities
Derivative Liabilities	505	322
Interest rate contracts
Derivative Assets
Derivative assets	1,765	773
Derivative Liabilities
Derivative Liabilities	217	133
Interest rate contracts | Derivatives designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional amount	26,800	29,846
Derivative Assets
Derivative assets	4	1
Derivative Liabilities
Derivative Liabilities	1	0
Interest rate contracts | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional amount	148,161	142,386
Derivative Assets
Derivative assets	1,761	772
Derivative Liabilities
Derivative Liabilities	216	133
Foreign exchange contracts
Derivative Assets
Derivative assets	239	174
Derivative Liabilities
Derivative Liabilities	189	166
Foreign exchange contracts | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional amount	16,448	15,101
Derivative Assets
Derivative assets	239	174
Derivative Liabilities
Derivative Liabilities	189	166
TBA contracts
Derivative Assets
Derivative assets	7
Derivative Liabilities
Derivative Liabilities	34
TBA contracts | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional amount	13,161	0
Derivative Assets
Derivative assets	7	0
Derivative Liabilities
Derivative Liabilities	34	0
Other contracts
Derivative Assets
Derivative assets	275	37
Derivative Liabilities
Derivative Liabilities	66	23
Other contracts | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional amount	8,011	6,868
Derivative Assets
Derivative assets	275	37
Derivative Liabilities
Derivative Liabilities	$ 66	$ 23