FAIR VALUE - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	$ 33,900	$ 33,750
Marketable equity securities	95	101
Total derivative assets	553	660
Total derivative liabilities	541	625
U.S. Treasury
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	13,150	13,903
Residential mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	16,605	15,620
Commercial mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	3,594	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	33,900	33,750
Marketable equity securities	95	101
Loans held for sale	70	55
Loans	23
Total derivative assets	553	660
Total derivative liabilities	541	625
Fair Value, Recurring | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	552	659
Total derivative liabilities	541	625
Fair Value, Recurring | Interest rate contracts | Qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	1	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	428	491
Total derivative liabilities	433	516
Fair Value, Recurring | Foreign exchange contract | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	108	152
Total derivative liabilities	107	108
Fair Value, Recurring | Other derivative | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	16	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	42	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	33,732	33,582
Marketable equity securities	53	53
Loans held for sale	70	55
Loans	23
Total derivative assets	534	643
Total derivative liabilities	540	624
Fair Value, Recurring | Level 2 | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	533	642
Total derivative liabilities	540	624
Fair Value, Recurring | Level 2 | Interest rate contracts | Qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	1	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	425	490
Total derivative liabilities	433	516
Fair Value, Recurring | Level 2 | Foreign exchange contract | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	108	152
Total derivative liabilities	107	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	168	168
Marketable equity securities	0	0
Loans held for sale	0	0
Loans	0
Total derivative assets	19	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	19	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	16	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	13,150	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	13,150	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	69	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	69	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	16,605	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	16,605	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	3,594	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	3,594	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	465	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	297	299
Fair Value, Recurring | Corporate bonds | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	168	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