BORROWED FUNDS - Long Term Debt (Details) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Long-term borrowed funds	[1]	$ 13,804	$ 13,467
Parent Company
Debt Instrument [Line Items]
Long-term borrowed funds		$ 4,591
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	60
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		$ 565	563
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	398
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	499
Parent Company | Senior Unsecured Notes | 5.841% fixed/floating-rate senior unsecured notes, due January 2030
Debt Instrument [Line Items]
Interest rate		5.841%
Long-term borrowed funds		$ 1,244	0
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		$ 747	746
CBNA and Other Subsidiaries
Debt Instrument [Line Items]
Long-term borrowed funds		$ 9,213
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	749
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		$ 650	649
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	599
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		$ 350	349
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		$ 480	483
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	798
CBNA and Other Subsidiaries | Federal Home Loan Bank advances
Debt Instrument [Line Items]
Weighted average rate		5.499%
Long-term borrowed funds		$ 2,036	3,786
CBNA and Other Subsidiaries | Secured Debt
Debt Instrument [Line Items]
Securitized borrowings, weighted average interest rate		5.479%
Long-term borrowed funds		$ 3,530	2,692
CBNA and Other Subsidiaries | Other
Debt Instrument [Line Items]
Long-term borrowed funds		$ 21	$ 18

[1] Includes amounts in consolidated VIEs. See Note 6 for additional information.