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BORROWED FUNDS - Narrative (Details) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Debt Instrument [Line Items]    
Short-term borrowed funds $ 10,529,000,000us-gaap_ShortTermBorrowings $ 7,042,000,000us-gaap_ShortTermBorrowings
Federal Home Loan Bank Advances and Letters of Credit [Member] | Secured Debt    
Debt Instrument [Line Items]    
Short-term borrowed funds 11,300,000,000us-gaap_ShortTermBorrowings
/ us-gaap_CreditFacilityAxis
= us-gaap_SecuredDebtMember
/ us-gaap_LongtermDebtTypeAxis
= cfg_FederalHomeLoanBankAdvancesandLettersofCreditMember		 4,200,000,000us-gaap_ShortTermBorrowings
/ us-gaap_CreditFacilityAxis
= us-gaap_SecuredDebtMember
/ us-gaap_LongtermDebtTypeAxis
= cfg_FederalHomeLoanBankAdvancesandLettersofCreditMember
Federal Home Loan advances    
Debt Instrument [Line Items]    
Available borrowing capacity 3,500,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FederalHomeLoanBankAdvancesMember		 8,200,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FederalHomeLoanBankAdvancesMember
Federal Reserve Bank Advances    
Debt Instrument [Line Items]    
Available borrowing capacity $ 26,300,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_FederalReserveBankAdvancesMember