REGULATORY MATTERS - Capital and Capital Ratio Information (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Common Equity Tier 1 to Risk-Weighted Assets (Amount)
Actual	$ 13,360cfg_Commonequitytier1capital
Minimum Capital Adequacy	4,940
Classification as Well-capitalized	7,136
Common Equity Tier 1 to Risk-Weighted Assets (Ratio)
Actual	12.20%cfg_CET1ratio
Minimum Capital Adequacy	4.50%
Classification as Well-capitalized	6.50%
Tier 1 Capital to Risk-Weighted Assets (Amount)
Actual	13,360us-gaap_TierOneRiskBasedCapital	13,173us-gaap_TierOneRiskBasedCapital
Minimum Capital Adequacy	6,587	4,239
Classification as Well-capitalized	8,783	6,358
Tier 1 Capital to Risk-Weighted Assets (Ratio)
Actual	12.20%	12.40%
Minimum Capital Adequacy	6.00%	4.00%
Classification as Well-capitalized	8.00%	6.00%
Total Capital to Risk-Weighted Assets (Amount)
Actual	16,969us-gaap_Capital	16,781us-gaap_Capital
Minimum Capital Adequacy	8,783	8,477
Classification as Well-capitalized	10,979	10,596
Total Capital to Risk-Weighted Assets (Ratio)
Actual	15.50%us-gaap_CapitalToRiskWeightedAssets	15.80%us-gaap_CapitalToRiskWeightedAssets
Minimum Capital Adequacy	8.00%	8.00%
Classification as Well-capitalized	10.00%	10.00%
Tier 1 Common Equity to Risk-Weighted Assets
Tier 1 Common Equity		13,173cfg_Tier1CommonEquity
Tier One Common Equity To Risk Weighted Assets		12.40%
Tier 1 Capital to Average Assets (Leverage) (Amount)
Actual	13,360us-gaap_TierOneLeverageCapital	13,173us-gaap_TierOneLeverageCapital
Minimum Capital Adequacy	5,087	4,982
Classification as Well-capitalized	$ 6,358	$ 6,227
Tier 1 Capital to Average Assets (Leverage) (Ratio)
Actual	10.50%	10.60%
Minimum Capital Adequacy	4.00%	4.00%
Classification as Well-capitalized	5.00%	5.00%

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Common equity tier 1 (“CET1”) divided by risk weighted assets as defined by regulations.

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Common equity tier 1 capital (“CETI”) as defined in the regulations under Basel III.

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The minimum amount of common equity tier 1 required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The minimum common equity tier 1 ratio (CET1 divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The common equity tier 1 ratio (CET1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

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Tier 1 Common Equity as defined in the regulations under Basel I.

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Tier 1 common equity divided by risk weighted assets as defined by regulations.

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The amount of total capital as defined in the regulations.

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The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

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Total Capital divided by risk weighted assets as defined in the regulations.

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Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

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The minimum amount of Tier 1 Leverage Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

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Tier 1 Leverage Capital divided by average assets as defined in the regulations.

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Tier 1 Risk Based Capital as defined in the regulations.

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The minimum amount of Tier 1 Risk Based Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

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Tier 1 capital divided by risk weighted assets as defined by regulations.

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