BUSINESS SEGMENTS - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) segment	Sep. 30, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment			2
Revenues	$ 1,443	$ 1,380	$ 4,223	$ 3,892
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