BORROWED FUNDS - Long Term Debt (Details) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Long-term borrowed funds	[1]	$ 13,467	$ 15,887
Parent company
Debt Instrument [Line Items]
Long-term borrowed funds		$ 3,344
Parent company | Subordinated Debt | 3.750% fixed-rate subordinated debt, due July 2024
Debt Instrument [Line Items]
Interest rate		3.75%
Long-term borrowed funds		$ 90	90
Parent company | Subordinated Debt | 4.023% fixed-rate subordinated debt, due October 2024
Debt Instrument [Line Items]
Interest rate		4.023%
Long-term borrowed funds		$ 17	17
Parent company | Subordinated Debt | 4.350% fixed-rate subordinated debt, due August 2025
Debt Instrument [Line Items]
Interest rate		4.35%
Long-term borrowed funds		$ 133	133
Parent company | Subordinated Debt | 4.300% fixed-rate subordinated debt, due December 2025
Debt Instrument [Line Items]
Interest rate		4.30%
Long-term borrowed funds		$ 336	336
Parent company | Subordinated Debt | 3.750% fixed-rate reset subordinated debt, due February 2031
Debt Instrument [Line Items]
Interest rate		3.75%
Long-term borrowed funds		$ 69	69
Parent company | Subordinated Debt | 4.300% fixed-rate reset subordinated debt, due February 2031
Debt Instrument [Line Items]
Interest rate		4.30%
Long-term borrowed funds		$ 135	135
Parent company | Subordinated Debt | 4.350% fixed-rate reset subordinated debt, due February 2031
Debt Instrument [Line Items]
Interest rate		4.35%
Long-term borrowed funds		$ 60	61
Parent company | Subordinated Debt | 2.638% fixed-rate subordinated debt, due September 2032
Debt Instrument [Line Items]
Interest rate		2.638%
Long-term borrowed funds		$ 563	556
Parent company | Subordinated Debt | 5.641% fixed-rate reset subordinated debt, due May 2037
Debt Instrument [Line Items]
Interest rate		5.641%
Long-term borrowed funds		$ 398	397
Parent company | Senior Unsecured Notes | 2.850% fixed-rate senior unsecured notes, due July 2026
Debt Instrument [Line Items]
Interest rate		2.85%
Long-term borrowed funds		$ 499	498
Parent company | Senior Unsecured Notes | 2.500% fixed-rate senior unsecured notes, due February 2030
Debt Instrument [Line Items]
Interest rate		2.50%
Long-term borrowed funds		$ 298	298
Parent company | Senior Unsecured Notes | 3.250% fixed-rate senior unsecured notes, due April 2030
Debt Instrument [Line Items]
Interest rate		3.25%
Long-term borrowed funds		$ 746	746
CBNA and Other Subsidiaries
Debt Instrument [Line Items]
Long-term borrowed funds		$ 10,123
CBNA and Other Subsidiaries | Senior Unsecured Notes | 3.700% senior unsecured notes, due March 2023
Debt Instrument [Line Items]
Interest rate		3.70%
Long-term borrowed funds		$ 0	497
CBNA and Other Subsidiaries | Senior Unsecured Notes | 5.676% floating-rate senior unsecured notes, due March 2023
Debt Instrument [Line Items]
Interest rate		5.676%
Long-term borrowed funds		$ 0	250
CBNA and Other Subsidiaries | Senior Unsecured Notes | 2.250% senior unsecured notes, due April 2025
Debt Instrument [Line Items]
Interest rate		2.25%
Long-term borrowed funds		$ 749	748
CBNA and Other Subsidiaries | Senior Unsecured Notes | 4.119% fixed/floating-rate senior unsecured notes, due May 2025
Debt Instrument [Line Items]
Interest rate		4.119%
Long-term borrowed funds		$ 649	648
CBNA and Other Subsidiaries | Senior Unsecured Notes | 6.064% fixed/floating-rate senior unsecured notes, due October 2025
Debt Instrument [Line Items]
Interest rate		6.064%
Long-term borrowed funds		$ 599	598
CBNA and Other Subsidiaries | Senior Unsecured Notes | 5.284% fixed/floating-rate senior unsecured notes, due January 2026
Debt Instrument [Line Items]
Interest rate		5.284%
Long-term borrowed funds		$ 349	0
CBNA and Other Subsidiaries | Senior Unsecured Notes | 3.750% senior unsecured notes, due February 2026
Debt Instrument [Line Items]
Interest rate		3.75%
Long-term borrowed funds		$ 483	475
CBNA and Other Subsidiaries | Senior Unsecured Notes | 4.575% fixed/floating-rate senior unsecured notes, due August 2028
Debt Instrument [Line Items]
Interest rate		4.575%
Long-term borrowed funds		$ 798	797
CBNA and Other Subsidiaries | Federal Home Loan advances
Debt Instrument [Line Items]
Weighted average interest rate		5.57%
Long-term borrowed funds		$ 3,786	8,519
CBNA and Other Subsidiaries | Secured Debt
Debt Instrument [Line Items]
Long-term borrowed funds		$ 2,692	0
Debt, Weighted Average Interest Rate		6.026%
CBNA and Other Subsidiaries | Other
Debt Instrument [Line Items]
Long-term borrowed funds		$ 18	$ 19

[1] Includes amounts in consolidated VIEs. See Note 11 for additional information.