LOAN SALES AND SECURITIZATIONS - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Residential Mortgage
Servicing Assets at Fair Value [Line Items]
Servicing income	$ 14	$ 12
Unpaid principal balance of third party serviced loans	19,100		$ 18,900
Automobile
Servicing Assets at Fair Value [Line Items]
Servicing income	5	2
Unpaid principal balance of third party serviced loans	1,300		1,700
Small Business Association (SBA) Loan
Servicing Assets at Fair Value [Line Items]
Servicing income	3	$ 2
Unpaid principal balance of third party serviced loans	$ 1,200		$ 1,100