GOODWILL AND INTANGIBLE ASSETS - Narrative (Details)	3 Months Ended
	Mar. 31, 2020 USD ($) reporting_unit	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Goodwill [Line Items]
Number of reporting units | reporting_unit	2
Goodwill acquired	$ 6,000,000
Goodwill impairment loss	0	$ 0
Amortization of intangibles	3,000,000	$ 2,000,000
Consumer Banking
Goodwill [Line Items]
Goodwill acquired	0
Goodwill accumulated impairment loss	5,900,000,000		$ 5,900,000,000
Commercial Banking
Goodwill [Line Items]
Goodwill acquired	6,000,000
Goodwill accumulated impairment loss	$ 50,000,000		$ 50,000,000