RELATED PARTY TRANSACTIONS AND SIGNIFICANT TRANSACTIONS WITH RBS - Schedule of Related Party Debt Terms (Details) - USD ($) $ in Millions					6 Months Ended
		Jul. 28, 2016	Mar. 07, 2016	Dec. 03, 2015	Jun. 30, 2016		Jun. 30, 2015	Dec. 31, 2015
Related Party Transaction [Line Items]
Long-term borrowed funds					$ 11,810			$ 9,886
Repurchase of long-term borrowed funds					3,631		$ 6
Citizens Financial Group, Inc.
Related Party Transaction [Line Items]
Long-term borrowed funds					$ 2,501
Subordinated Debt | 5.158% fixed-to-floating rate subordinated debt, (LIBOR 3.56%) callable, due 2023 | Citizens Financial Group, Inc.
Related Party Transaction [Line Items]
Interest rate	[1]				5.158%
Long-term borrowed funds	[1]				$ 333			$ 333
Subordinated Debt | 3.750% fixed rate subordinated debt, due 2024 | Citizens Financial Group, Inc.
Related Party Transaction [Line Items]
Interest rate	[1]				3.75%	[2]		4.153%
Long-term borrowed funds	[1],[2]				$ 250			$ 250
Subordinated Debt | 4.023% fixed rate subordinated debt, due 2024 | Citizens Financial Group, Inc.
Related Party Transaction [Line Items]
Interest rate	[1],[3]				4.023%
Long-term borrowed funds	[1],[3]				$ 218			331
Extinguishment of debt, amount			$ 125
Subordinated Debt | 4.082% fixed rate subordinated debt, due 2025 | Citizens Financial Group, Inc.
Related Party Transaction [Line Items]
Interest rate	[1],[4]				4.082%
Long-term borrowed funds	[1],[4]				$ 355			$ 331
RBSG
Related Party Transaction [Line Items]
Repurchase of long-term borrowed funds			$ 125	$ 750
RBSG | Subsequent Event
Related Party Transaction [Line Items]
Repurchase of long-term borrowed funds		$ 500
RBSG | Subordinated Debt | 5.158% fixed-to-floating rate subordinated debt, (LIBOR 3.56%) callable, due 2023
Related Party Transaction [Line Items]
Interest rate					5.158%			5.158%
Long-term borrowed funds					$ 333			$ 333
RBSG | Subordinated Debt | 3.750% fixed rate subordinated debt, due 2024
Related Party Transaction [Line Items]
Interest rate	[5]				3.75%
Long-term borrowed funds					$ 250
RBSG | Subordinated Debt | 4.153% fixed rate subordinated debt, due 2024
Related Party Transaction [Line Items]
Interest rate								4.153%
Long-term borrowed funds								$ 250
RBSG | Subordinated Debt | 4.023% fixed rate subordinated debt, due 2024
Related Party Transaction [Line Items]
Interest rate					4.023%	[6],[7]		4.023%
Long-term borrowed funds					$ 208			$ 333
RBSG | Subordinated Debt | 4.023% fixed rate subordinated debt, due 2024 | Subsequent Event
Related Party Transaction [Line Items]
Interest rate		4.023%
Repurchase of long-term borrowed funds		$ 166
RBSG | Subordinated Debt | 4.082% fixed rate subordinated debt, due 2025
Related Party Transaction [Line Items]
Interest rate					4.082%	[6]		4.082%
Long-term borrowed funds					$ 334			$ 334
RBSG | Subordinated Debt | 4.082% fixed rate subordinated debt, due 2025 | Subsequent Event
Related Party Transaction [Line Items]
Interest rate		4.082%
Repurchase of long-term borrowed funds		$ 334

[1] Borrowed funds with RBS as of December 31, 2015. See Note 13 “Related Party Transactions and Significant Transactions with RBS” for further information.

[2] Prior to January 1, 2016, interest was payable at a fixed rate per annum of 4.153%.

[3] These balances are comprised of: principal balance of $208 million and $333 million at June 30, 2016 and December 31, 2015, respectively, as well as the impact from interest rate swaps of $10 million and ($2) million at June 30, 2016 and December 31, 2015, respectively. See Note 11 “Derivatives” for further information. In addition, on March 7, 2016, the Company repurchased $125 million of these securities from RBS. See Note 13 “Related Party Transactions and Significant Transactions with RBS” for further information.

[4] These balances are comprised of: principal balance of $334 million at June 30, 2016 and December 31, 2015; impact from interest rate swaps of $21 million and ($3) million at June 30, 2016 and December 31, 2015, respectively. See Note 11 “Derivatives” for further information.

[5] Prior to January 1, 2016, interest was payable at a fixed rate per annum of 4.153%.

[6] On July 28, 2016, the Company repurchased $500 million of its subordinated notes held by RBS, including $166 million of its 4.023% subordinated notes due 2024 and $334 million of its 4.082% subordinated notes due 2025. Refer to Note 21 “Subsequent Events” for further information.

[7] On March 7, 2016, the Company repurchased $125 million of these securities from RBS.