FAIR VALUE - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	$ 28,190	$ 19,936
Marketable equity securities	82	84
Total derivative assets	553	640
Total derivative liabilities	507	636
U.S. Treasury
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	11,817	10,508
Residential mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	13,016	6,686
Commercial mortgage-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	2,778	2,131
Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	17	12
Fair Value, Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	28,190	19,936
Marketable equity securities	82	84
Loans held for sale	41	38
Total derivative assets	553	640
Total derivative liabilities	507	636
Fair Value, Recurring | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	553	640
Total derivative liabilities	507	636
Fair Value, Recurring | 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 | Interest rate contracts | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	446	530
Total derivative liabilities	415	518
Fair Value, Recurring | Foreign exchange contract | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	93	104
Total derivative liabilities	91	117
Fair Value, Recurring | Other derivative | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	14	6
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	31	36
Loans held for sale	0	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	28,026	19,779
Marketable equity securities	51	48
Loans held for sale	41	38
Total derivative assets	538	633
Total derivative liabilities	506	635
Fair Value, Recurring | Level 2 | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	538	633
Total derivative liabilities	506	635
Fair Value, Recurring | Level 2 | 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 2 | Interest rate contracts | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	445	529
Total derivative liabilities	415	518
Fair Value, Recurring | Level 2 | Foreign exchange contract | Non-qualifying Hedges
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total derivative assets	93	104
Total derivative liabilities	91	117
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	164	157
Marketable equity securities	0	0
Loans held for sale	0	0
Total derivative assets	15	7
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	15	7
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	1	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	14	6
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	11,817	10,508
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	11,817	10,508
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	85	117
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	85	117
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	13,016	6,686
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	13,016	6,686
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	2,778	2,131
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	2,778	2,131
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	477	482
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	313	325
Fair Value, Recurring | Corporate Bonds | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	164	157
Fair Value, Recurring | Municipal bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	17	12
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	12
Fair Value, Recurring | Municipal bonds | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investment securities available for sale	$ 0	$ 0