DERIVATIVES - Schedule of Derivative Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Derivative Assets
Derivative assets	$ 2,486	$ 984
Less: Gross amounts offset in the Consolidated Balance Sheets	(286)	(107)
Less: Cash collateral applied	(232)	(70)
Total net derivative fair values presented in the Consolidated Balance Sheets	1,968	807
Derivative Liabilities
Derivative Liabilities	860	322
Less: Gross amounts offset in the Consolidated Balance Sheets	(286)	(107)
Less: Cash collateral applied	(340)	(95)
Total net derivative fair values presented in the Consolidated Balance Sheets	234	120
Derivatives not designated as hedging instruments:
Derivative Assets
Derivative assets	2,477	983
Derivative Liabilities
Derivative Liabilities	856	322
Interest rate contracts
Derivative Assets
Derivative assets	1,799	773
Derivative Liabilities
Derivative Liabilities	209	133
Interest rate contracts | Derivatives designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional amount	30,050	29,846
Derivative Assets
Derivative assets	9	1
Derivative Liabilities
Derivative Liabilities	4	0
Interest rate contracts | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional amount	146,035	142,386
Derivative Assets
Derivative assets	1,790	772
Derivative Liabilities
Derivative Liabilities	205	133
Foreign exchange contracts
Derivative Assets
Derivative assets	413	174
Derivative Liabilities
Derivative Liabilities	361	166
Foreign exchange contracts | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional amount	15,974	15,101
Derivative Assets
Derivative assets	413	174
Derivative Liabilities
Derivative Liabilities	361	166
TBA contracts
Derivative Assets
Derivative assets	42
Derivative Liabilities
Derivative Liabilities	202
TBA contracts | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional amount	14,568	0
Derivative Assets
Derivative assets	42	0
Derivative Liabilities
Derivative Liabilities	202	0
Other contracts
Derivative Assets
Derivative assets	232	37
Derivative Liabilities
Derivative Liabilities	88	23
Other contracts | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional amount	6,706	6,868
Derivative Assets
Derivative assets	232	37
Derivative Liabilities
Derivative Liabilities	$ 88	$ 23