CASH AND DUE FROM BANKS (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Deposits on FRB balances	$ 11,700	$ 2,100
Interest rate on FRB balances	0.10%
Interest earned on FRB balances	$ 10	$ 28	$ 28

Interest-Bearing Cash and Due from Banks, Federal Reserve Bank Balances

No definition available.

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