BUSINESS SEGMENTS - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) segment	Sep. 30, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment			2
Revenues	$ 1,380	$ 1,209	$ 3,892	$ 3,592
Consumer Banking
Segment Reporting Information [Line Items]
Revenues	850	791	2,460	2,317
Consumer Banking | Maximum
Segment Reporting Information [Line Items]
Revenues			25
Commercial Banking
Segment Reporting Information [Line Items]
Revenues	$ 450	$ 399	1,285	$ 1,169
Commercial Banking | Minimum
Segment Reporting Information [Line Items]
Revenues			25
Commercial Banking | Maximum
Segment Reporting Information [Line Items]
Revenues			$ 2,500