BORROWED FUNDS - Long Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Long-term borrowed funds	$ 18,855	$ 15,887
Parent Company
Debt Instrument [Line Items]
Long-term borrowed funds	$ 3,338
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	$ 558	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	$ 498	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	$ 15,517
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	$ 748	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	$ 648	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	$ 598	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	$ 449	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	$ 481	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	$ 797	797
CBNA and Other Subsidiaries | Federal Home Loan Bank advances
Debt Instrument [Line Items]
Weighted average rate	4.873%
Long-term borrowed funds	$ 11,779	8,519
CBNA and Other Subsidiaries | Other
Debt Instrument [Line Items]
Long-term borrowed funds	$ 17	$ 19