ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Modifications [Line Items]
Mortgage loans collateralized by OREO	$ 216	$ 257
Larger balance commercial loans minimum balance (greater than)	3	3
Other loans held for sale	386	40
Commitments to lend additional funds to debtors owing receivables which were TDRs	$ 28	$ 15
High loan to value criteria (exceeds)	90.00%	90.00%
Total commercial
Financing Receivable, Modifications [Line Items]
TDR balance	$ 143	$ 155
Total retail
Financing Receivable, Modifications [Line Items]
TDR balance	775	$ 1,200
TDR Loans
Financing Receivable, Modifications [Line Items]
Other loans held for sale	373
TDR Loans \| Residential mortgages
Financing Receivable, Modifications [Line Items]
Other loans held for sale	288
TDR Loans \| Home equity loans
Financing Receivable, Modifications [Line Items]
Other loans held for sale	$ 85

Minimum qualifying carrying balance of commercial loans.

No definition available.

Name:	cfg_CommercialLoansLargeBalanceMinimumQualifyingBalance
Namespace Prefix:	cfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

An entity's internal risk assessment as having high risk defined as certain loans with outstanding balances exceeding a percentage of the value of underlying collateral.

+ References

No definition available.

+ Details

Name:	cfg_CreditRiskHighLoantoValueLoansPercentExceedingValueOfUnderlyingCollateral
Namespace Prefix:	cfg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Recorded investment in financing receivables that are on nonaccrual status and are collateralized by land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	cfg_MortgageloanscollateralizedbyOREO
Namespace Prefix:	cfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of other loans receivable that will be sold to other entities.

+ References

No definition available.

+ Details

Name:	cfg_OtherLoansReceivableHeldforsaleAmount
Namespace Prefix:	cfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

TDR balance included in impaired loans.

+ References

No definition available.

+ Details

Name:	cfg_TDRBalanceIncludedinImpairedLoans.
Namespace Prefix:	cfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Reflects the unfunded portion of contractual agreements to lend funds to borrowers for loans whose terms have been modified by troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18794-111554

+ Details

Name:	us-gaap_LoansAndLeasesReceivableImpairedCommitmentToLend
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Details

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

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=cfg_ImpairedLoansMember
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: