FAIR VALUE - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	$ 34,963	$ 33,750
Marketable equity securities	110	101
Total derivative assets	570	660
Total derivative liabilities	520	625
U.S. Treasury
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	13,781	13,903
Residential mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	17,435	15,620
Commercial mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	3,428	3,666
Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	17	17
Fair Value, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	34,963	33,750
Marketable equity securities	110	101
Loans held for sale	80	55
Loans	22
Total derivative assets	570	660
Total derivative liabilities	520	625
Fair Value, Recurring | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	570	659
Total derivative liabilities	520	625
Fair Value, Recurring | Interest rate contracts | Qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	0	1
Total derivative liabilities	0	0
Fair Value, Recurring | Interest rate contracts | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	403	491
Total derivative liabilities	383	516
Fair Value, Recurring | Foreign exchange contract | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	145	152
Total derivative liabilities	136	108
Fair Value, Recurring | Other derivative | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	22	16
Total derivative liabilities	1	1
Fair Value, Recurring | Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	0	0
Marketable equity securities	46	48
Loans held for sale	0	0
Loans	0
Total derivative assets	0	0
Total derivative liabilities	0	0
Fair Value, Recurring | Level 1 | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Fair Value, Recurring | Level 1 | Interest rate contracts | Qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Fair Value, Recurring | Level 1 | Interest rate contracts | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Fair Value, Recurring | Level 1 | Foreign exchange contract | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Fair Value, Recurring | Level 1 | Other derivative | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Fair Value, Recurring | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	34,854	33,582
Marketable equity securities	64	53
Loans held for sale	80	55
Loans	22
Total derivative assets	545	643
Total derivative liabilities	519	624
Fair Value, Recurring | Level 2 | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	545	642
Total derivative liabilities	519	624
Fair Value, Recurring | Level 2 | Interest rate contracts | Qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	0	1
Total derivative liabilities	0	0
Fair Value, Recurring | Level 2 | Interest rate contracts | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	400	490
Total derivative liabilities	383	516
Fair Value, Recurring | Level 2 | Foreign exchange contract | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	145	152
Total derivative liabilities	136	108
Fair Value, Recurring | Level 2 | Other derivative | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Fair Value, Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	109	168
Marketable equity securities	0	0
Loans held for sale	0	0
Loans	0
Total derivative assets	25	17
Total derivative liabilities	1	1
Fair Value, Recurring | Level 3 | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	25	17
Total derivative liabilities	1	1
Fair Value, Recurring | Level 3 | Interest rate contracts | Qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Fair Value, Recurring | Level 3 | Interest rate contracts | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	3	1
Total derivative liabilities	0	0
Fair Value, Recurring | Level 3 | Foreign exchange contract | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	0	0
Total derivative liabilities	0	0
Fair Value, Recurring | Level 3 | Other derivative | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	22	16
Total derivative liabilities	1	1
Fair Value, Recurring | U.S. Treasury
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	13,781	13,903
Fair Value, Recurring | U.S. Treasury | Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	0	0
Fair Value, Recurring | U.S. Treasury | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	13,781	13,903
Fair Value, Recurring | U.S. Treasury | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	0	0
Fair Value, Recurring | Government agency
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	52	77
Fair Value, Recurring | Government agency | Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	0	0
Fair Value, Recurring | Government agency | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	52	77
Fair Value, Recurring | Government agency | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	0	0
Fair Value, Recurring | Residential mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	17,435	15,620
Fair Value, Recurring | Residential mortgage-backed securities | Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	0	0
Fair Value, Recurring | Residential mortgage-backed securities | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	17,435	15,620
Fair Value, Recurring | Residential mortgage-backed securities | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	0	0
Fair Value, Recurring | Commercial mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	3,428	3,666
Fair Value, Recurring | Commercial mortgage-backed securities | Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	0	0
Fair Value, Recurring | Commercial mortgage-backed securities | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	3,428	3,666
Fair Value, Recurring | Commercial mortgage-backed securities | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	0	0
Fair Value, Recurring | Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	250	467
Fair Value, Recurring | Corporate bonds | Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	0	0
Fair Value, Recurring | Corporate bonds | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	141	299
Fair Value, Recurring | Corporate bonds | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	109	168
Fair Value, Recurring | Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	17	17
Fair Value, Recurring | Municipal bonds | Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	0	0
Fair Value, Recurring | Municipal bonds | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	17	17
Fair Value, Recurring | Municipal bonds | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	$ 0	$ 0