FAIR VALUE - Schedule of Carrying Values and Estimated Fair Values for Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financial Assets
Investment in marketable equity securities	$ 79	$ 84
Investment securities available for sale	24,915	19,936
Investment securities held to maturity	10,050	9,979
Interest rate & other derivative — non-qualifying hedges	659	640
Financial Liabilities
Fair value of derivative financial instruments	654	636
Carrying Value
Financial Assets
Cash and due from banks	698	908
Interest-earning deposits at banks	30,792	33,609
Securities purchased under agreements to resell	394	473
Investment in marketable equity securities	79	84
Investment securities available for sale	24,915	19,936
Investment securities held to maturity	10,050	9,979
Loans held for sale	83	73
Net loans	131,613	129,545
Accrued interest receivable	914	832
Federal Home Loan Bank stock	20	20
Mortgage servicing rights	25	25
Financial Liabilities
Deposits with no stated maturity	132,601	129,427
Time deposits	17,008	16,427
Credit balances of factoring clients	1,152	1,089
Securities sold under customer repurchase agreements	395	485
Long-term borrowings	37,137	37,160
Accrued interest payable	141	137
Carrying Value | Qualifying Hedges
Financial Assets
Interest rate & other derivative — non-qualifying hedges	0	0
Financial Liabilities
Fair value of derivative financial instruments	0	0
Carrying Value | Non-qualifying Hedges
Financial Assets
Interest rate & other derivative — non-qualifying hedges	659	640
Financial Liabilities
Fair value of derivative financial instruments	654	636
Estimated Fair Value
Financial Assets
Cash and due from banks	698	908
Interest-earning deposits at banks	30,792	33,609
Securities purchased under agreements to resell	394	473
Investment in marketable equity securities	79	84
Investment securities available for sale	24,915	19,936
Investment securities held to maturity	8,479	8,503
Loans held for sale	84	73
Net loans	128,564	126,696
Accrued interest receivable	914	832
Federal Home Loan Bank stock	20	20
Mortgage servicing rights	44	42
Financial Liabilities
Deposits with no stated maturity	132,601	129,427
Time deposits	17,013	16,416
Credit balances of factoring clients	1,152	1,089
Securities sold under customer repurchase agreements	395	485
Long-term borrowings	36,421	36,816
Accrued interest payable	141	137
Estimated Fair Value | Level 1
Financial Assets
Cash and due from banks	698	908
Interest-earning deposits at banks	30,792	33,609
Securities purchased under agreements to resell	0	0
Investment in marketable equity securities	32	36
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	394	473
Investment in marketable equity securities	47	48
Investment securities available for sale	24,754	19,779
Investment securities held to maturity	8,479	8,503
Loans held for sale	50	38
Net loans	1,507	1,479
Accrued interest receivable	914	832
Federal Home Loan Bank stock	20	20
Mortgage servicing rights	0	0
Financial Liabilities
Deposits with no stated maturity	132,601	129,427
Time deposits	17,013	16,416
Credit balances of factoring clients	0	0
Securities sold under customer repurchase agreements	395	485
Long-term borrowings	36,421	36,816
Accrued interest payable	141	137
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	161	157
Investment securities held to maturity	0	0
Loans held for sale	34	35
Net loans	127,057	125,217
Accrued interest receivable	0	0
Federal Home Loan Bank stock	0	0
Mortgage servicing rights	44	42
Financial Liabilities
Deposits with no stated maturity	0	0
Time deposits	0	0
Credit balances of factoring clients	1,152	1,089
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
Interest rate & other derivative — non-qualifying hedges	0	0
Financial Liabilities
Fair value of derivative financial instruments	0	0
Estimated Fair Value | Qualifying Hedges | Level 1
Financial Assets
Interest rate & other derivative — non-qualifying hedges	0	0
Financial Liabilities
Fair value of derivative financial instruments	0	0
Estimated Fair Value | Qualifying Hedges | Level 2
Financial Assets
Interest rate & other derivative — non-qualifying hedges	0	0
Financial Liabilities
Fair value of derivative financial instruments	0	0
Estimated Fair Value | Qualifying Hedges | Level 3
Financial Assets
Interest rate & other derivative — non-qualifying hedges	0	0
Financial Liabilities
Fair value of derivative financial instruments	0	0
Estimated Fair Value | Non-qualifying Hedges
Financial Assets
Interest rate & other derivative — non-qualifying hedges	659	640
Financial Liabilities
Fair value of derivative financial instruments	654	636
Estimated Fair Value | Non-qualifying Hedges | Level 1
Financial Assets
Interest rate & other derivative — non-qualifying hedges	0	0
Financial Liabilities
Fair value of derivative financial instruments	0	0
Estimated Fair Value | Non-qualifying Hedges | Level 2
Financial Assets
Interest rate & other derivative — non-qualifying hedges	650	633
Financial Liabilities
Fair value of derivative financial instruments	653	635
Estimated Fair Value | Non-qualifying Hedges | Level 3
Financial Assets
Interest rate & other derivative — non-qualifying hedges	9	7
Financial Liabilities
Fair value of derivative financial instruments	$ 1	$ 1