GOODWILL AND CORE DEPOSIT INTANGIBLES - Schedule of Goodwill (Details) $ in Millions	12 Months Ended
Dec. 31, 2025 USD ($)
Intangible Asset, Finite-Lived, Acquired [Line Items]
Balance at January 1	$ 346
Balance at end of period	346
BMO Bank
Intangible Asset, Finite-Lived, Acquired [Line Items]
BMO Branch Acquisition goodwill	$ 0

Amount, after accumulated impairment loss, of asset representing future economic benefit arising from other asset acquired in business combination or from joint venture formation or both, that is not individually identified and separately recognized.

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+ Details