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INVESTMENT SECURITIES - Schedule of Interest and Dividends on Investment Securities (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Investments [Abstract] |  |  |  |
Interest income - taxable investment securities | $ 432 | $ 357 | $ 1,263 | $ 967
Interest income - nontaxable investment securities | 1 | 0 | 1 | 1
Dividend income - marketable equity securities | 0 | 1 | 2 | 2
Interest on investment securities | $ 433 | $ 358 | $ 1,266 | $ 970

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- Definition Amount of operating interest income, including amortization and accretion of premiums and discounts, on securities subject to state, federal and other income tax. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-K (SK) -Number 229 -Section 1402 -Paragraph a -Publisher SEC Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478524/942-220-S99-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Regulation S-K (SK) -Number 229 -Section 1402 -Paragraph b -Subparagraph (1)(Instruction 4) -Publisher SEC + Details
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