COMMITMENTS AND CONTINGENCIES - Narrative (Details) $ in Millions	1 Months Ended		9 Months Ended		12 Months Ended		21 Months Ended
	Aug. 31, 2015 USD ($)	Apr. 30, 2013 USD ($)	Sep. 30, 2015 USD ($) counterparty	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2003	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)
Letters of Credit [Abstract]
Letters of credit outstanding			$ 1.0		$ 3.0		$ 1.0
Risk Participation Agreements [Abstract]
Risk participation agreements			$ 39.0		19.0		39.0
Risk participation agreements number of counterparties | counterparty			78
Risk participation agreements, Maximum term			10 years
Consumer Products [Abstract]
Litigation settlement amount	$ 20.5
Mortgage Repurchase Demands [Abstract]
Mortgage repurchase demands received							35.0
Indemnification payment requests received							5.0
Repurchased mortgage loans			$ 9.0	$ 22.0			34.0
Indemnification payment requests paid			0.0	7.0			8.0
Payments for Repurchase of Mortgage Loans			9.0	$ 22.0
Consent Orders
Consumer Products [Abstract]
Litigation settlement amount		$ 10.0
Restitution amount payable		$ 8.0
Commercial real estate loans held for sale | Purchase Commitment
Commitments [Abstract]
Unsettled commercial loan trades			134.0				134.0
Loans and Leases Receivable, Commitments to Purchase or Sell			$ 170.0
Minimum
Risk Participation Agreements [Abstract]
Risk participation agreements, Average term			1 year
Maximum
Risk Participation Agreements [Abstract]
Risk participation agreements, Average term			5 years
Marketing rights
Marketing Rights [Abstract]
Commitment period						25 years
Payments made			$ 3.0		$ 3.0
Remaining obligation due			$ 47.0				47.0
Student
Commitments [Abstract]
Purchase obligation, cumulative maximum amount								$ 700.0
Purchase obligation, period from original agreement date after which no termination fee is payable			3 years
Student | Minimum
Commitments [Abstract]
Purchase commitment, due in next twelve months								100.0
Student | Maximum
Commitments [Abstract]
Purchase commitment, due in next twelve months								$ 163.0
Automobile | Minimum
Commitments [Abstract]
Purchase commitment, due in next twelve months			$ 250.0				250.0
Purchase commitment, due after next twelve months			50.0				50.0
Automobile | Maximum
Commitments [Abstract]
Purchase commitment, due in next twelve months			600.0				600.0
Purchase commitment, due after next twelve months			$ 200.0				$ 200.0
Financial standby letters of credit
Letters of Credit [Abstract]
Guarantor Obligations, Term			10 years
Commercial letters of credit
Letters of Credit [Abstract]
Guarantor Obligations, Term			1 year