GOODWILL AND INTANGIBLE ASSETS - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) reporting_unit	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 01, 2019 USD ($)	Jan. 01, 2019 USD ($)
Goodwill [Line Items]
Number of reporting units | reporting_unit	2
Goodwill impairment	$ 0	$ 0	$ 0
Amortization of intangible assets	11	3	$ 0
Consumer Banking
Goodwill [Line Items]
Goodwill accumulated impairment loss	5,900	5,900
Commercial Banking
Goodwill [Line Items]
Goodwill accumulated impairment loss	50	$ 50
Clarfeld
Goodwill [Line Items]
Goodwill acquired during period	83
Intangible assets acquired					$ 21
Bowstring
Goodwill [Line Items]
Goodwill acquired during period	35
Intangible assets acquired				$ 6
Other | Clarfeld
Goodwill [Line Items]
Intangible assets acquired	19
Other | Bowstring
Goodwill [Line Items]
Intangible assets acquired	5
Naming Rights
Goodwill [Line Items]
Intangible assets acquired	$ 18