BUSINESS SEGMENTS - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($) segment	Mar. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segment	2
Revenues	$ 1,234	$ 1,183
Consumer Banking
Segment Reporting Information [Line Items]
Revenues	789	752
Consumer Banking | Maximum
Segment Reporting Information [Line Items]
Revenues	25
Commercial Banking
Segment Reporting Information [Line Items]
Revenues	399	$ 376
Commercial Banking | Minimum
Segment Reporting Information [Line Items]
Revenues	25
Commercial Banking | Maximum
Segment Reporting Information [Line Items]
Revenues	$ 2,500