BORROWED FUNDS - Long Term Debt (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term borrowed funds		$ 11,765	$ 12,790
Banking Subsidiaries
Debt Instrument [Line Items]
Long-term borrowed funds		9,445
Citizens Financial Group, Inc.
Debt Instrument [Line Items]
Long-term borrowed funds		$ 2,320
Senior Unsecured Notes | Banking Subsidiaries | 2.300% senior unsecured notes, due 2018
Debt Instrument [Line Items]
Interest rate		2.30%
Long-term borrowed funds	[1],[2]	$ 0	745
Senior Unsecured Notes | Banking Subsidiaries | 2.450% senior unsecured notes, due 2019
Debt Instrument [Line Items]
Interest rate		2.45%
Long-term borrowed funds	[1]	$ 743	747
Senior Unsecured Notes | Banking Subsidiaries | 2.500% senior unsecured notes, due 2019
Debt Instrument [Line Items]
Interest rate		2.50%
Long-term borrowed funds	[1]	$ 741	741
Senior Unsecured Notes | Banking Subsidiaries | 2.250% senior unsecured notes, due 2020 (1)
Debt Instrument [Line Items]
Interest rate		2.25%
Long-term borrowed funds	[1]	$ 692	0
Senior Unsecured Notes | Banking Subsidiaries | Floating rate senior unsecured notes, due 2020
Debt Instrument [Line Items]
Long-term borrowed funds	[1]	299	0
Senior Unsecured Notes | Banking Subsidiaries | Floating rate senior unsecured notes, due 2020
Debt Instrument [Line Items]
Long-term borrowed funds	[1]	$ 249	0
Senior Unsecured Notes | Banking Subsidiaries | 2.200% senior unsecured notes, due 2020
Debt Instrument [Line Items]
Interest rate		2.20%
Long-term borrowed funds	[1]	$ 498	0
Senior Unsecured Notes | Banking Subsidiaries | 2.250% senior unsecured notes, due 2020
Debt Instrument [Line Items]
Interest rate		2.25%
Long-term borrowed funds	[1]	$ 742	0
Senior Unsecured Notes | Banking Subsidiaries | 2.550% senior unsecured notes, due 2021
Debt Instrument [Line Items]
Interest rate		2.55%
Long-term borrowed funds	[1]	$ 964	965
Senior Unsecured Notes | Banking Subsidiaries | Floating-rate senior unsecured notes, due 2022
Debt Instrument [Line Items]
Long-term borrowed funds	[1]	$ 249	0
Senior Unsecured Notes | Banking Subsidiaries | 2.650% senior unsecured notes, due 2022
Debt Instrument [Line Items]
Interest rate		2.65%
Long-term borrowed funds	[1]	$ 491	0
Senior Unsecured Notes | Citizens Financial Group, Inc. | 2.375% fixed rate senior unsecured debt, due 2021
Debt Instrument [Line Items]
Interest rate		2.375%
Long-term borrowed funds		$ 349	348
Subordinated Debt | Citizens Financial Group, Inc. | 4.150% fixed rate subordinated debt, due 2022
Debt Instrument [Line Items]
Interest rate		4.15%
Long-term borrowed funds		$ 348	347
Subordinated Debt | Citizens Financial Group, Inc. | 5.158% fixed-to-floating rate subordinated debt, (LIBOR 3.56%) callable, due 2023
Debt Instrument [Line Items]
Interest rate		5.158%
Long-term borrowed funds		$ 333	333
Subordinated Debt | Citizens Financial Group, Inc. | 3.750% fixed rate subordinated debt due 2024
Debt Instrument [Line Items]
Interest rate		3.75%
Long-term borrowed funds		$ 250	250
Subordinated Debt | Citizens Financial Group, Inc. | 4.023% fixed rate subordinated debt, due 2024
Debt Instrument [Line Items]
Interest rate		4.023%
Long-term borrowed funds		$ 42	42
Subordinated Debt | Citizens Financial Group, Inc. | 4.350% fixed rate subordinated debt, due 2025
Debt Instrument [Line Items]
Interest rate		4.35%
Long-term borrowed funds		$ 249	249
Subordinated Debt | Citizens Financial Group, Inc. | 4.300% fixed rate subordinated debt, due 2025
Debt Instrument [Line Items]
Interest rate		4.30%
Long-term borrowed funds		$ 749	749
Subordinated Debt | Citizens Financial Group, Inc. | LIBOR | 5.158% fixed-to-floating rate subordinated debt, (LIBOR 3.56%) callable, due 2023
Debt Instrument [Line Items]
Interest rate		3.56%
Federal Home Loan advances | Banking Subsidiaries
Debt Instrument [Line Items]
Long-term borrowed funds		$ 3,761	7,264
Other | Banking Subsidiaries
Debt Instrument [Line Items]
Long-term borrowed funds		$ 16	$ 10

[1] Issued under CBNA’s Global Bank Note Program

[2] Reclassified to short-term borrowed funds.