BUSINESS SEGMENTS - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) segment	Jun. 30, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment			2
Revenues	$ 1,396	$ 1,278	$ 2,780	$ 2,512
Consumer Banking
Segment Reporting Information [Line Items]
Revenues	886	821	1,744	1,610
Consumer Banking | Maximum
Segment Reporting Information [Line Items]
Revenues			25
Commercial Banking
Segment Reporting Information [Line Items]
Revenues	$ 474	$ 436	954	$ 835
Commercial Banking | Minimum
Segment Reporting Information [Line Items]
Revenues			25
Commercial Banking | Maximum
Segment Reporting Information [Line Items]
Revenues			$ 2,500