BUSINESS OPERATING SEGMENTS - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment			2
Revenues	$ 1,509	$ 1,396	$ 2,971	$ 2,780
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