GOODWILL AND INTANGIBLE ASSETS - Narrative (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2021 USD ($) reportingUnit	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Goodwill [Line Items]
Number of reporting units | reportingUnit		2
Goodwill impairment	$ 0	$ 0	$ 0	$ 0
Amortization of intangible assets		11,000,000	11,000,000	$ 11,000,000
Consumer Banking
Goodwill [Line Items]
Goodwill accumulated impairment loss	5,900,000,000	5,900,000,000	5,900,000,000
Commercial Banking
Goodwill [Line Items]
Goodwill accumulated impairment loss	$ 50,000,000	$ 50,000,000	$ 50,000,000