FAIR VALUE MEASUREMENTS - Schedule of Financial Instruments not Recorded at Fair Value (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity	$ 5,178us-gaap_HeldToMaturitySecurities	$ 5,148us-gaap_HeldToMaturitySecurities
Securities held-to-maturity	5,281	5,193
Other investment securities	867	872
Other investment securities	867cfg_OtherInvestmentSecurities	872cfg_OtherInvestmentSecurities
Other loans held for sale	54	25
Other loans held for sale	54	25
Loans and leases	94,494	93,410
Loans and leases	94,892	93,674
Deposits	98,990us-gaap_Deposits	95,707us-gaap_Deposits
Deposits	99,005us-gaap_DepositsFairValueDisclosure	95,710us-gaap_DepositsFairValueDisclosure
Federal funds purchased and securities sold under agreements to repurchase	4,421	4,276
Federal funds purchased and securities sold under agreements to repurchase	4,421	4,276
Other short-term borrowed funds	7,004us-gaap_OtherShortTermBorrowings	6,253us-gaap_OtherShortTermBorrowings
Other short-term borrowed funds	7,004	6,253
Long-term borrowed funds	3,904us-gaap_LongTermDebt	4,642us-gaap_LongTermDebt
Long-term borrowed funds	4,006us-gaap_LongTermDebtFairValue	4,706us-gaap_LongTermDebtFairValue
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity	5,178	5,148
Other investment securities	867	872
Other loans held for sale	54	25
Loans and leases	94,494	93,410
Deposits	98,990	95,707
Federal funds purchased and securities sold under agreements to repurchase	4,421	4,276
Other short-term borrowed funds	7,004	6,253
Long-term borrowed funds	3,904	4,642
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held-to-maturity	0	0
Other investment securities	0	0
Other loans held for sale	0	0
Loans and leases	0	0
Deposits	0	0
Federal funds purchased and securities sold under agreements to repurchase	0	0
Other short-term borrowed funds	0	0
Long-term borrowed funds	0	0
Level 1 \| Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity	0	0
Other investment securities	0	0
Other loans held for sale	0	0
Loans and leases	0	0
Deposits	0	0
Federal funds purchased and securities sold under agreements to repurchase	0	0
Other short-term borrowed funds	0	0
Long-term borrowed funds	0	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held-to-maturity	5,281	5,193
Other investment securities	867	872
Other loans held for sale	0	0
Loans and leases	87	102
Deposits	99,005	95,710
Federal funds purchased and securities sold under agreements to repurchase	4,421	4,276
Other short-term borrowed funds	7,004	6,253
Long-term borrowed funds	4,006	4,706
Level 2 \| Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity	5,178	5,148
Other investment securities	867	872
Other loans held for sale	0	0
Loans and leases	87	102
Deposits	98,990	95,707
Federal funds purchased and securities sold under agreements to repurchase	4,421	4,276
Other short-term borrowed funds	7,004	6,253
Long-term borrowed funds	3,904	4,642
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held-to-maturity	0	0
Other investment securities	0	0
Other loans held for sale	54	25
Loans and leases	94,805	93,572
Deposits	0	0
Federal funds purchased and securities sold under agreements to repurchase	0	0
Other short-term borrowed funds	0	0
Long-term borrowed funds	0	0
Level 3 \| Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity	0	0
Other investment securities	0	0
Other loans held for sale	54	25
Loans and leases	94,407	93,308
Deposits	0	0
Federal funds purchased and securities sold under agreements to repurchase	0	0
Other short-term borrowed funds	0	0
Long-term borrowed funds	$ 0	$ 0

Fair value of other investment securities.

No definition available.

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- Definition

The amortized cost as of the balance sheet date of other investment securities.

+ References

No definition available.

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- Definition

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

+ References

No definition available.

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Fair value portion of other loans receivable held-for-sale.

+ References

No definition available.

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Fair value portion of short-term borrowings not otherwise specified in the taxonomy having initial terms less than one year or the normal operating cycle, if longer.

+ References

No definition available.

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- Definition

The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.12)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 12

-Article 9

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- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

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- Definition

Fair value portion of short term borrowing where a bank borrows, at the federal funds rate, from another bank and securities that an entity sells and agrees to repurchase at a specified date for a specified price.

+ References

No definition available.

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- Definition

Amount after offset of short term borrowing where a bank borrows, at the federal funds rate, from another bank and securities that an entity sells and agrees to repurchase at a specified date for a specified price.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.13(1))

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 13

-Subparagraph 1

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- Definition

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (f)

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-SubTopic 10

-Section 25

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Fair value of investments in debt securities classified as held-to-maturity.

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- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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-Publisher FASB

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-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Glossary Loan

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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 7

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-Paragraph 1

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-Paragraph 1

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

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Sum of the carrying amounts at the balance sheet date of short-term borrowings not otherwise specified in the taxonomy having initial terms less than one year or the normal operating cycle, if longer.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Article 5

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-Publisher FASB

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-Topic 210

-SubTopic 10

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-Paragraph 1

-Subparagraph (SX 210.5-02.19(a)(7))

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