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VARIABLE INTEREST ENTITIES - Narrative (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Variable Interest Entity [Line Items]  
Investment in Low Income Housing Tax Credit Partnerships $ 469cfg_AmortizationMethodQualifiedAffordableHousingProjectInvestments
Gross Investment in Low Income Housing Tax Credit Partnerships 481cfg_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsGross
Accumulated Amortization Qualified Affordable Housing Project Investments 12cfg_AccumulatedAmortizationQualifiedAffordableHousingProjectInvestments
Qualified Affordable Housing Project Investments, Commitment 319cfg_QualifiedAffordableHousingProjectInvestmentsCommitment
Amortization Method Qualified Affordable Housing Project Investments, Amortization 12cfg_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsAmortization
Affordable Housing Tax Credits and Other Tax Benefits, Amount 11cfg_AffordableHousingTaxCreditsandOtherTaxBenefitsAmount
LIHTC Investments  
Variable Interest Entity [Line Items]  
Other Tax Expense (Benefit) $ 4us-gaap_OtherTaxExpenseBenefit
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= cfg_QualifiedAffordableHousingInvestmentMember