CASH AND DUE FROM BANKS (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Abstract]
Interest-bearing cash and due from banks	$ 2,045	$ 2,749
Interest rate on FRB balances	1.50%
Interest earned on FRB balances	$ 16	$ 7	$ 4

For banks and other depository institutions (including Federal Reserve Banks, if applicable): Interest-bearing cash in other financial institutions for relatively short periods of time including, for example, certificates of deposits, which are presented separately from cash on the balance sheet.

No definition available.

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