ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Default of Modified Debt Agreements (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2016 USD ($) contract	Sep. 30, 2015 USD ($) contract	Sep. 30, 2016 USD ($) contract	Sep. 30, 2015 USD ($) contract
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	311	298	788	936
Balance Defaulted \| $	$ 13	$ 21	$ 39	$ 47
Commercial Banking
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	5	7	17	21
Balance Defaulted \| $	$ 1	$ 1	$ 4	$ 2
Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	5	7	16	21
Balance Defaulted \| $	$ 1	$ 1	$ 4	$ 2
Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	0	0	1	0
Balance Defaulted \| $	$ 0	$ 0	$ 0	$ 0
Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	306	291	771	915
Balance Defaulted \| $	$ 12	$ 20	$ 35	$ 45
Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	57	37	146	120
Balance Defaulted \| $	$ 7	$ 7	$ 19	$ 18
Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	14	47	39	130
Balance Defaulted \| $	$ 0	$ 6	$ 3	$ 12
Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	48	26	93	98
Balance Defaulted \| $	$ 4	$ 3	$ 8	$ 6
Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	7	11	28	34
Balance Defaulted \| $	$ 0	$ 1	$ 1	$ 2
Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	3	10	14	17
Balance Defaulted \| $	$ 0	$ 1	$ 0	$ 1
Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	43	24	80	66
Balance Defaulted \| $	$ 0	$ 0	$ 1	$ 1
Student
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	15	33	46	142
Balance Defaulted \| $	$ 0	$ 1	$ 1	$ 3
Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	117	102	323	304
Balance Defaulted \| $	$ 1	$ 1	$ 2	$ 2
Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	2	1	2	4
Balance Defaulted \| $	$ 0	$ 0	$ 0	$ 0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableModificationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cfg_CommercialBankingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cfg_RetailMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cfg_ConsumerHomeEquityLoanServicedbyOthersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cfg_ConsumerHomeEquityLineofCreditServicedbyOthersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_AutomobileLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cfg_ConsumerStudentLoansReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CreditCardReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cfg_ConsumerOtherRetailMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: