INVESTMENT SECURITIES (Narrative) (Details)	3 Months Ended	12 Months Ended
Mar. 31, 2026 USD ($) security	Mar. 31, 2025 USD ($)	Dec. 31, 2025 USD ($) security
Marketable Securities [Line Items]
Accrued interest receivable	$ 57,000,000		$ 64,000,000
Investment securities	19,071,000,000		$ 19,220,000,000
Unrealized loss amortization associated with the securities transferred from AFS to HTM	$ 40,000,000	$ 43,000,000
Number of AFS investment securities in an unrealized loss position \| security	2,005		2,037
Available-for-sale, gross gains	$ 0	0
Available-for-sale, gross losses	0	$ 0
Allowance for credit loss on HTM securities (less than)	1,000,000
Fixed-Rate Available For Sale Securities
Marketable Securities [Line Items]
Unrealized loss amortization associated with the securities transferred from AFS to HTM, before tax	1,500,000,000		$ 1,600,000,000
Unrealized loss amortization associated with the securities transferred from AFS to HTM	1,200,000,000		1,200,000,000
Asset Pledged as Collateral
Marketable Securities [Line Items]
Investment securities	$ 17,200,000,000		$ 17,500,000,000

Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Amount, excluding accrued interest, of allowance for credit loss on investment in debt security measured at amortized cost (held-to-maturity).

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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