BUSINESS OPERATING SEGMENTS - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment	2
Revenues	$ 5,707	$ 5,255	$ 4,824
Consumer Banking | Maximum
Segment Reporting Information [Line Items]
Revenues	25
Commercial Banking | Minimum
Segment Reporting Information [Line Items]
Revenues	25
Commercial Banking | Maximum
Segment Reporting Information [Line Items]
Revenues	$ 2,500