REGULATORY MATTERS - Capital and Capital Ratio Information (Details) $ in Millions	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Common Equity Tier 1 to Risk-Weighted Assets (Amount)
Actual	$ 18,240	$ 17,900
Required Minimum Capital	$ 15,434	$ 14,913
Common Equity Tier 1 to Risk-Weighted Assets (Ratio)
Actual	0.106	0.108
Required Minimum Capital	9.00%	9.00%
Tier 1 Capital to Risk-Weighted Assets (Amount)
Actual	$ 20,351
Required Minimum Capital	$ 18,007	$ 17,398
Tier 1 Capital to Risk-Weighted Assets (Ratio)
Actual	0.119	0.121
Required Minimum Capital	0.105	0.105
Total Capital to Risk-Weighted Assets (Amount)
Actual	$ 23,654	$ 23,232
Required Minimum Capital	$ 21,437	$ 20,712
Total Capital to Risk-Weighted Assets (Ratio)
Actual	0.138	0.140
Required Minimum Capital	0.125	0.125
Tier 1 Capital to Average Assets (Leverage) (Amount)
Actual		$ 20,013
Required Minimum Capital	$ 8,613	$ 8,502
Tier 1 Capital to Average Assets (Leverage) (Ratio)
Actual	0.095	0.094
Required Minimum Capital	0.040	0.040
Stress capital buffer	4.50%	4.50%
CBNA
Common Equity Tier 1 to Risk-Weighted Assets (Amount)
Actual	$ 20,946	$ 20,250
Required Minimum Capital	$ 11,946	$ 11,549
Common Equity Tier 1 to Risk-Weighted Assets (Ratio)
Actual	0.123	0.123
Required Minimum Capital	7.00%	7.00%
Tier 1 Capital to Risk-Weighted Assets (Amount)
Actual	$ 20,946
Required Minimum Capital	$ 14,506	$ 14,024
Tier 1 Capital to Risk-Weighted Assets (Ratio)
Actual	0.123	0.123
Required Minimum Capital	0.085	0.085
Total Capital to Risk-Weighted Assets (Amount)
Actual	$ 24,135	$ 23,362
Required Minimum Capital	$ 17,919	$ 17,324
Total Capital to Risk-Weighted Assets (Ratio)
Actual	0.141	0.142
Required Minimum Capital	0.105	0.105
Tier 1 Capital to Average Assets (Leverage) (Amount)
Actual		$ 20,250
Required Minimum Capital	$ 8,572	$ 8,474
Tier 1 Capital to Average Assets (Leverage) (Ratio)
Actual	0.098	0.096
Required Minimum Capital	0.040	0.040
Capital conservation buffer	2.50%	2.50%