GOODWILL AND CORE DEPOSIT INTANGIBLES - Schedule of Changes in Core Deposit Intangibles (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
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| Finite-lived Intangible Assets [Roll Forward] | ||||
| Less: amortization for the period | $ 14 | $ 13 | $ 38 | $ 41 |
| Core Deposits | ||||
| Finite-lived Intangible Assets [Roll Forward] | ||||
| Balance at beginning of period, net of accumulated amortization | 195 | |||
| Less: amortization for the period | 38 | |||
| Balance at end of period, net of accumulated amortization | $ 349 | 349 | ||
| Core Deposits | BMO Bank | ||||
| Finite-lived Intangible Assets [Roll Forward] | ||||
| BMO Branch Acquisition core deposit intangibles | $ 192 | |||
| X | ||||||||||
- Definition Amount of amortization expense for finite-lived intangible asset. Excludes goodwill and capitalized cost for software to be sold, leased, or marketed. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Amount, after accumulated amortization, of finite-lived intangible asset. Excludes goodwill and capitalized cost for software to be sold, leased, or marketed. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. No definition available.
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- Definition Amount of increase in finite-lived intangible asset acquired in business combination, asset acquisition, and from joint venture formation. Excludes goodwill and capitalized cost for software to be sold, leased, or marketed. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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