COMMITMENTS AND CONTINGENCIES - Narrative (Details)		3 Months Ended	9 Months Ended	12 Months Ended
	Jan. 07, 2016 USD ($)	Mar. 31, 2016 USD ($) counterparty	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2003	Nov. 30, 2015 USD ($)
Letters of Credit [Abstract]
Letters of credit outstanding		$ 3,000,000		$ 3,000,000
Risk Participation Agreements [Abstract]
Risk participation agreements		$ 53,000,000		26,000,000
Risk participation agreements number of counterparties | counterparty		89
Risk participation agreements, Maximum term		10 years
Commitments [Abstract]
Long-term borrowed funds		$ 10,035,000,000		9,886,000,000
Commercial real estate loans held for sale | Purchase commitment
Commitments [Abstract]
Unsettled commercial loan trade purchases		98,000,000
Unsettled commercial loan trade sales		125,000,000
Citizens Financial Group, Inc.
Commitments [Abstract]
Long-term borrowed funds		$ 2,487,000,000
Subordinated Debt | Citizens Financial Group, Inc. | Purchase commitment
Commitments [Abstract]
Long-term borrowed funds						$ 500,000,000
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		$ 0		$ 3,000,000
Remaining obligation due		47,000,000
Automobile | Minimum
Commitments [Abstract]
Purchase commitment, due after next twelve months		50,000,000
Automobile | Maximum
Commitments [Abstract]
Purchase commitment, due after next twelve months		$ 200,000,000
Student
Commitments [Abstract]
Termination fee	$ 1,000,000
Student | Minimum
Commitments [Abstract]
Purchase commitment, due in next twelve months	125,000,000
Aggregate purchase principal balance	500,000,000
Student | Maximum
Commitments [Abstract]
Aggregate purchase principal balance	$ 1,000,000,000
Financial standby letters of credit
Letters of Credit [Abstract]
Letters of credit terms		10 years
Commercial letters of credit
Letters of Credit [Abstract]
Letters of credit terms		1 year
Scenario, Forecast | Marketing rights
Marketing Rights [Abstract]
Payments made			$ 3,000,000