SUBSEQUENT EVENTS - Narrative (Details) - USD ($)				3 Months Ended		6 Months Ended
	Aug. 03, 2015	Jul. 21, 2015	Apr. 07, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jul. 31, 2015
Subsequent Event [Line Items]
Dividends declared and paid (in Dollars per Share)				$ 0.10	$ 0.61	$ 0.20	$ 0.66
Dividends paid to common stockholders						$ 48,000,000
RBSG
Subsequent Event [Line Items]
Treasury stock purchased, price per share (in dollars per share)			$ 23.87			$ 25.48
Subsequent Event
Subsequent Event [Line Items]
RBS sale of CFG's common stock (in shares)	98,900,000
Percent of outstanding common stock held by RBS prior to sale of shares	18.40%
Sale of Shares by Controlling Shareholder, Share Price	$ 26.00
Outstanding common stock held by RBS (in shares)	110,461,782
Percent of outstanding common stock held by RBS	20.90%
Dividends declared and paid (in Dollars per Share)		$ 0.10
Dividends paid to common stockholders		$ 53,000,000
Subsequent Event | RBSG
Subsequent Event [Line Items]
Treasury stock purchased, price per share (in dollars per share)	$ 26.00
Treasury stock purchased (in shares)	9,615,384
Subsequent Event | Subordinated Debt | 4.350% Fixed Rate Subordinated Debt, Due 2025
Subsequent Event [Line Items]
Aggregate principal amount of debt								$ 250,000,000
Interest rate								4.35%