DERIVATIVES - Schedule of Derivative Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2025	Mar. 31, 2025	Dec. 31, 2024
Derivatives, Fair Value [Line Items]
Notional Amount	$ 305,510		$ 279,484
Derivative Assets
Derivative assets	1,523		1,476
Less: Gross amounts offset in the Consolidated Balance Sheets	(379)		(391)
Less: Cash collateral applied	(423)		(677)
Total net derivatives presented in the Consolidated Balance Sheets	721		408
Derivative Liabilities
Derivative liabilities	1,286		1,710
Less: Gross amounts offset in the Consolidated Balance Sheets	(379)		(391)
Less: Cash collateral applied	(169)		(99)
Total net derivatives presented in the Consolidated Balance Sheets	738		1,220
Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional Amount	233,073		210,407
Derivative Assets
Derivative assets	1,220		1,074
Derivative Liabilities
Derivative liabilities	1,284		1,705
Interest rate contracts
Derivative Assets
Derivative assets	492		562
Derivative Liabilities
Derivative liabilities	489		910
Interest rate contracts | Cash Flow Hedging
Derivatives, Fair Value [Line Items]
Notional Amount	466	$ 1,500
Interest rate contracts | Derivatives designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional Amount	72,437		69,077
Derivative Assets
Derivative assets	303		402
Derivative Liabilities
Derivative liabilities	2		5
Interest rate contracts | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional Amount	183,555		171,193
Derivative Assets
Derivative assets	189		160
Derivative Liabilities
Derivative liabilities	487		905
Foreign exchange contracts
Derivative Assets
Derivative assets	563		472
Derivative Liabilities
Derivative liabilities	399		411
Foreign exchange contracts | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional Amount	42,050		34,749
Derivative Assets
Derivative assets	563		472
Derivative Liabilities
Derivative liabilities	399		411
Commodities contracts
Derivative Assets
Derivative assets	438		429
Derivative Liabilities
Derivative liabilities	381		379
Commodities contracts | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional Amount	1,213		1,136
Derivative Assets
Derivative assets	438		429
Derivative Liabilities
Derivative liabilities	381		379
TBA contracts
Derivative Assets
Derivative assets	7		10
Derivative Liabilities
Derivative liabilities	13		8
TBA contracts | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional Amount	5,034		2,714
Derivative Assets
Derivative assets	7		10
Derivative Liabilities
Derivative liabilities	13		8
Other contracts
Derivative Assets
Derivative assets	23		3
Derivative Liabilities
Derivative liabilities	4		2
Other contracts | Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Notional Amount	1,221		615
Derivative Assets
Derivative assets	23		3
Derivative Liabilities
Derivative liabilities	$ 4		$ 2