SECURITIES - Schedule of Investments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Equity Securities Available-for-sale, Amortized Cost	$ 18,433	$ 16,010
Equity Securities Available-for-sale, Gross Unrealized Gains	308	159
Equity Securities Available-for-sale, Gross Unrealized Losses	(85)	(174)
Equity Securities Available-for-sale, Fair Value	18,656us-gaap_AvailableForSaleSecurities	15,995us-gaap_AvailableForSaleSecurities
Securities Held-to-maturity, Amortized Cost	5,148us-gaap_HeldToMaturitySecurities	4,315us-gaap_HeldToMaturitySecurities
Securities Held-to-maturity, Gross Unrealized Gain	76	0
Securities Held-to-maturity, Gross Unrealized Losses	(31)	(58)
Securities held-to-maturity, Fair Value	5,193	4,257
Other Investment Securities, Amortized Cost	872	935
Other Investment Securities, Gross Unrealized Gains	0	0
Other Investment Securities, Gross Unrealized Losses	0	0
Other Investment Securities, Fair Value	872cfg_OtherInvestmentSecurities	935cfg_OtherInvestmentSecurities
U.S. Treasury
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost	15	15
Debt Securities Available-for-sale, Gross Unrealized Gains	0	0
Debt Securities Available-for-sale, Gross Unrealized Losses	0	0
Debt Securities Available-for-sale, Fair Value	15	15
State and political subdivisions
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost	10	11
Debt Securities Available-for-sale, Gross Unrealized Gains	0	0
Debt Securities Available-for-sale, Gross Unrealized Losses	0	(1)
Debt Securities Available-for-sale, Fair Value	10	10
Federal agencies and U.S. government sponsored entities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost	17,683	14,970
Debt Securities Available-for-sale, Gross Unrealized Gains	301	151
Debt Securities Available-for-sale, Gross Unrealized Losses	(50)	(128)
Debt Securities Available-for-sale, Fair Value	17,934	14,993
Securities Held-to-maturity, Amortized Cost	3,728	2,940
Securities Held-to-maturity, Gross Unrealized Gain	22	0
Securities Held-to-maturity, Gross Unrealized Losses	(31)	(33)
Securities held-to-maturity, Fair Value	3,719	2,907
Other/non-agency
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost	703	992
Debt Securities Available-for-sale, Gross Unrealized Gains	4	5
Debt Securities Available-for-sale, Gross Unrealized Losses	(35)	(45)
Debt Securities Available-for-sale, Fair Value	672	952
Securities Held-to-maturity, Amortized Cost	1,420	1,375
Securities Held-to-maturity, Gross Unrealized Gain	54	0
Securities Held-to-maturity, Gross Unrealized Losses	0	(25)
Securities held-to-maturity, Fair Value	1,474	1,350
Total mortgage-backed securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost	18,386	15,962
Debt Securities Available-for-sale, Gross Unrealized Gains	305	156
Debt Securities Available-for-sale, Gross Unrealized Losses	(85)	(173)
Debt Securities Available-for-sale, Fair Value	18,606	15,945
Total debt securities available for sale
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Debt Securities Available-for-sale, Amortized Cost	18,411	15,988
Debt Securities Available-for-sale, Gross Unrealized Gains	305	156
Debt Securities Available-for-sale, Gross Unrealized Losses	(85)	(174)
Debt Securities Available-for-sale, Fair Value	18,631	15,970
Marketable equity securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Equity Securities Available-for-sale, Amortized Cost	10	10
Equity Securities Available-for-sale, Gross Unrealized Gains	3	3
Equity Securities Available-for-sale, Gross Unrealized Losses	0	0
Equity Securities Available-for-sale, Fair Value	13	13
Other equity securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Equity Securities Available-for-sale, Amortized Cost	12	12
Equity Securities Available-for-sale, Gross Unrealized Gains	0	0
Equity Securities Available-for-sale, Gross Unrealized Losses	0	0
Equity Securities Available-for-sale, Fair Value	12	12
Total equity securities available for sale
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Equity Securities Available-for-sale, Amortized Cost	22	22
Equity Securities Available-for-sale, Gross Unrealized Gains	3	3
Equity Securities Available-for-sale, Gross Unrealized Losses	0	0
Equity Securities Available-for-sale, Fair Value	25	25
Federal Reserve Bank stock
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Federal Reserve Bank Stock, Amortized Cost	477	462
Federal Reserve Bank Stock, Gross Unrealized Gains	0	0
Federal Reserve Bank Stock, Gross Unrealized Loss	0	0
Federal Reserve Bank Stock, Fair Value	477	462
Federal Home Loan Bank stock
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Federal Home Loan Bank Stock, Amortized Cost	390	468
Federal Home Loan Bank Stock, Gross Unrealized Gain	0	0
Federal Home Loan Bank Stock, Gross Unrealized Loss	0	0
Federal Home Loan Bank Stock, Fair Value	390	468
Total other investment securities
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items]
Venture Capital, Amortized Cost	5	5
Venture Capital, Gross Unrealized Gain	0	0
Venture Capital, Gross Unrealized Loss	0	0
Venture Capital, Fair Value	$ 5	$ 5

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Amount of accumulated unrealized loss on Federal Home Loan Bank stock.

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Fair value of Federal Home Loan Bank (FHLB) stock.

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Amount of accumulated unrealized gain on firm holdings in private equity, mezzanine, venture capital, merchant banking, real estate and special situations investments. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

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Amount of accumulated unrealized loss on firm holdings in private equity, mezzanine, venture capital, merchant banking, real estate and special situations investments. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

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The amortized cost as of the balance sheet date of firm holdings in private equity, mezzanine, venture capital, merchant banking, real estate and special situations investments. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

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Fair value of other investment securities.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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

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