REGULATORY MATTERS - Capital and Capital Ratio Information (Details) $ in Millions	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Common Equity Tier 1 to Risk-Weighted Assets (Amount)
Actual	$ 17,900	$ 18,358
Required Minimum Capital	$ 14,913	$ 14,671
Common Equity Tier 1 to Risk-Weighted Assets (Ratio)
Actual	0.108	0.106
Required Minimum Capital	9.00%	8.50%
Tier 1 Capital to Risk-Weighted Assets (Amount)
Actual	$ 20,013	$ 20,372
Required Minimum Capital	$ 17,398	$ 17,260
Tier 1 Capital to Risk-Weighted Assets (Ratio)
Actual	0.121	0.118
Required Minimum Capital	0.105	0.100
Total Capital to Risk-Weighted Assets (Amount)
Actual	$ 23,232	$ 23,608
Required Minimum Capital	$ 20,712	$ 20,712
Total Capital to Risk-Weighted Assets (Ratio)
Actual	0.140	0.137
Required Minimum Capital	0.125	0.120
Tier 1 Capital to Average Assets (Leverage) (Amount)
Actual	$ 20,013	$ 20,372
Required Minimum Capital	$ 8,502	$ 8,784
Tier 1 Capital to Average Assets (Leverage) (Ratio)
Actual	0.094	0.093
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	$ 20,250	$ 19,411
Required Minimum Capital	$ 11,549	$ 12,047
Common Equity Tier 1 to Risk-Weighted Assets (Ratio)
Actual	0.123	0.113
Required Minimum Capital	7.00%	7.00%
Tier 1 Capital to Risk-Weighted Assets (Amount)
Actual	$ 20,250	$ 19,411
Required Minimum Capital	$ 14,024	$ 14,628
Tier 1 Capital to Risk-Weighted Assets (Ratio)
Actual	0.123	0.113
Required Minimum Capital	0.085	0.085
Total Capital to Risk-Weighted Assets (Amount)
Actual	$ 23,362	$ 22,453
Required Minimum Capital	$ 17,324	$ 18,070
Total Capital to Risk-Weighted Assets (Ratio)
Actual	0.142	0.130
Required Minimum Capital	0.105	0.105
Tier 1 Capital to Average Assets (Leverage) (Amount)
Actual	$ 20,250	$ 19,411
Required Minimum Capital	$ 8,474	$ 8,759
Tier 1 Capital to Average Assets (Leverage) (Ratio)
Actual	0.096	0.089
Required Minimum Capital	0.040	0.040
Capital conservation buffer	2.50%	2.50%