FAIR VALUE - Schedule of Carrying Values and Estimated Fair Values for Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Financial Assets
Investment in marketable equity securities	$ 110	$ 101
Investment securities available for sale	34,963	33,750
Investment securities held to maturity	10,051	10,239
Fair value of derivative financial instruments	570	660
Financial Liabilities
Fair value of derivative financial instruments	520	625
Carrying Value
Financial Assets
Cash and due from banks	874	814
Interest-earning deposits at banks	24,798	21,364
Securities purchased under agreements to resell	83	158
Investment in marketable equity securities	110	101
Investment securities available for sale	34,963	33,750
Investment securities held to maturity	10,051	10,239
Loans held for sale	110	82
Net loans	141,074	136,567
Accrued interest receivable	945	902
Federal Home Loan Bank stock	20	20
Mortgage servicing rights	30	27
Financial Liabilities
Deposits with no stated maturity	152,116	141,976
Time deposits	11,074	13,253
Credit balances of factoring clients	1,326	1,016
Securities sold under customer repurchase agreements	423	367
Long-term borrowings	38,185	36,669
Accrued interest payable	105	134
Carrying Value | Qualifying Hedges
Financial Assets
Fair value of derivative financial instruments		1
Carrying Value | Non-qualifying Hedges
Financial Assets
Fair value of derivative financial instruments	570	659
Financial Liabilities
Fair value of derivative financial instruments	520	625
Estimated Fair Value
Financial Assets
Cash and due from banks	874	814
Interest-earning deposits at banks	24,798	21,364
Securities purchased under agreements to resell	83	158
Investment in marketable equity securities	110	101
Investment securities available for sale	34,963	33,750
Investment securities held to maturity	8,838	8,702
Loans held for sale	110	82
Net loans	141,924	134,872
Accrued interest receivable	945	902
Federal Home Loan Bank stock	20	20
Mortgage servicing rights	48	47
Financial Liabilities
Deposits with no stated maturity	152,116	141,976
Time deposits	11,058	13,247
Credit balances of factoring clients	1,326	1,016
Securities sold under customer repurchase agreements	423	367
Long-term borrowings	38,211	36,220
Accrued interest payable	105	134
Estimated Fair Value | Level 1
Financial Assets
Cash and due from banks	874	814
Interest-earning deposits at banks	24,798	21,364
Securities purchased under agreements to resell	0	0
Investment in marketable equity securities	46	48
Investment securities available for sale	0	0
Investment securities held to maturity	0	0
Loans held for sale	0	0
Net loans	0	0
Accrued interest receivable	0	0
Federal Home Loan Bank stock	0	0
Mortgage servicing rights	0	0
Financial Liabilities
Deposits with no stated maturity	0	0
Time deposits	0	0
Credit balances of factoring clients	0	0
Securities sold under customer repurchase agreements	0	0
Long-term borrowings	0	0
Accrued interest payable	0	0
Estimated Fair Value | Level 2
Financial Assets
Cash and due from banks	0	0
Interest-earning deposits at banks	0	0
Securities purchased under agreements to resell	83	158
Investment in marketable equity securities	64	53
Investment securities available for sale	34,854	33,582
Investment securities held to maturity	8,838	8,702
Loans held for sale	80	55
Net loans	1,618	1,463
Accrued interest receivable	945	902
Federal Home Loan Bank stock	20	20
Mortgage servicing rights	0	0
Financial Liabilities
Deposits with no stated maturity	152,116	141,976
Time deposits	11,058	13,247
Credit balances of factoring clients	0	0
Securities sold under customer repurchase agreements	423	367
Long-term borrowings	38,211	36,220
Accrued interest payable	105	134
Estimated Fair Value | Level 3
Financial Assets
Cash and due from banks	0	0
Interest-earning deposits at banks	0	0
Securities purchased under agreements to resell	0	0
Investment in marketable equity securities	0	0
Investment securities available for sale	109	168
Investment securities held to maturity	0	0
Loans held for sale	30	27
Net loans	140,306	133,409
Accrued interest receivable	0	0
Federal Home Loan Bank stock	0	0
Mortgage servicing rights	48	47
Financial Liabilities
Deposits with no stated maturity	0	0
Time deposits	0	0
Credit balances of factoring clients	1,326	1,016
Securities sold under customer repurchase agreements	0	0
Long-term borrowings	0	0
Accrued interest payable	0	0
Estimated Fair Value | Qualifying Hedges
Financial Assets
Fair value of derivative financial instruments		1
Estimated Fair Value | Qualifying Hedges | Level 1
Financial Assets
Fair value of derivative financial instruments		0
Estimated Fair Value | Qualifying Hedges | Level 2
Financial Assets
Fair value of derivative financial instruments		1
Estimated Fair Value | Qualifying Hedges | Level 3
Financial Assets
Fair value of derivative financial instruments		0
Estimated Fair Value | Non-qualifying Hedges
Financial Assets
Fair value of derivative financial instruments	570	659
Financial Liabilities
Fair value of derivative financial instruments	520	625
Estimated Fair Value | Non-qualifying Hedges | Level 1
Financial Assets
Fair value of derivative financial instruments	0	0
Financial Liabilities
Fair value of derivative financial instruments	0	0
Estimated Fair Value | Non-qualifying Hedges | Level 2
Financial Assets
Fair value of derivative financial instruments	545	642
Financial Liabilities
Fair value of derivative financial instruments	519	624
Estimated Fair Value | Non-qualifying Hedges | Level 3
Financial Assets
Fair value of derivative financial instruments	25	17
Financial Liabilities
Fair value of derivative financial instruments	$ 1	$ 1