GOODWILL AND OTHER INTANGIBLES - Schedule of Goodwill by Reporting Units (Details) $ in Millions	9 Months Ended
Sep. 30, 2026 USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 2,767.0
Additions during the period	6,478.0
Goodwill, ending balance	9,245.0
Auto
Goodwill [Roll Forward]
Goodwill, beginning balance	1,239.0
Additions during the period	0.0
Goodwill, ending balance	1,239.0
CBB
Goodwill [Roll Forward]
Goodwill, beginning balance	159.0
Additions during the period	1,500.0
Goodwill, ending balance	1,659.0
Commercial Banking
Goodwill [Roll Forward]
Goodwill, beginning balance	1,067.0
Additions during the period	4,978.0
Goodwill, ending balance	6,045.0
CIB
Goodwill [Roll Forward]
Goodwill, beginning balance	302.0
Additions during the period	0.0
Goodwill, ending balance	302.0
C&I
Goodwill [Roll Forward]
Goodwill, beginning balance	52.0
CRE
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 1,000.0

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