BUSINESS SEGMENTS - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) segment	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment	2
Revenues	$ 4,824	$ 4,979	$ 4,690
Consumer Banking
Segment Reporting Information [Line Items]
Revenues	3,108	3,050	3,201
Consumer Banking | Maximum
Segment Reporting Information [Line Items]
Revenues	25
Commercial Banking
Segment Reporting Information [Line Items]
Revenues	1,577	$ 1,502	$ 1,420
Commercial Banking | Minimum
Segment Reporting Information [Line Items]
Revenues	25
Commercial Banking | Maximum
Segment Reporting Information [Line Items]
Revenues	$ 2,500