FAIR VALUE MEASUREMENTS - Nonrecurring Fair Value Measurements Narrative (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average life (in years)	5 years 2 months 12 days	5 years 4 months 24 days
Weighted average constant prepayment rate (percent)	12.40%	13.00%
Weighted average discount rate (percent)	9.80%	10.80%
Transfers between Levels 1, 2, or 3	$ 0cfg_FairValueTransfersBetweenLevels	$ 0cfg_FairValueTransfersBetweenLevels	$ 0cfg_FairValueTransfersBetweenLevels
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average life (in years)	2 years 9 months 18 days	1 year 9 months 18 days
Weighted average constant prepayment rate (percent)	10.40%	9.40%
Weighted average discount rate (percent)	9.10%	10.20%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average life (in years)	6 years 7 months 6 days	7 years 4 months 24 days
Weighted average constant prepayment rate (percent)	22.60%	41.50%
Weighted average discount rate (percent)	12.10%	13.10%

Amount of transfer of financial instrument classified as an asset between levels 1, 2 or 3 during the period.

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- Definition

Discount rate used to estimate the fair value of servicing assets and servicing liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 2

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122596-111746

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- Definition

Estimated rate of prepayments of principal on servicing assets and servicing liabilities.

+ References

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- Definition

Weighted average life of financial assets and financial liabilities, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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