REGULATORY MATTERS - Capital and Capital Ratio Information (Details) $ in Millions	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Common Equity Tier 1 to Risk-Weighted Assets (Amount)
Actual	$ 18,358	$ 18,574
Required Minimum Capital	$ 14,671	$ 14,633
Common Equity Tier 1 to Risk-Weighted Assets (Ratio)
Actual	0.106	0.100
Required Minimum Capital	8.50%	7.90%
Tier 1 Capital to Risk-Weighted Assets (Amount)
Actual	$ 20,372	$ 20,588
Required Minimum Capital	$ 17,260	$ 17,411
Tier 1 Capital to Risk-Weighted Assets (Ratio)
Actual	0.118	0.111
Required Minimum Capital	0.100	0.094
Total Capital to Risk-Weighted Assets (Amount)
Actual	$ 23,608	$ 23,755
Required Minimum Capital	$ 20,712	$ 21,116
Total Capital to Risk-Weighted Assets (Ratio)
Actual	0.137	0.128
Required Minimum Capital	0.120	0.114
Tier 1 Capital to Average Assets (Leverage) (Amount)
Actual	$ 20,372	$ 20,588
Required Minimum Capital	$ 8,784	$ 8,831
Tier 1 Capital to Average Assets (Leverage) (Ratio)
Actual	0.093	0.093
Required Minimum Capital	0.040	0.040
Stress capital buffer	4.00%	4.00%
CBNA
Common Equity Tier 1 to Risk-Weighted Assets (Amount)
Actual	$ 19,411	$ 20,669
Required Minimum Capital	$ 12,047	$ 12,935
Common Equity Tier 1 to Risk-Weighted Assets (Ratio)
Actual	0.113	0.112
Required Minimum Capital	7.00%	7.00%
Tier 1 Capital to Risk-Weighted Assets (Amount)
Actual	$ 19,411	$ 20,669
Required Minimum Capital	$ 14,628	$ 15,706
Tier 1 Capital to Risk-Weighted Assets (Ratio)
Actual	0.113	0.112
Required Minimum Capital	0.085	0.085
Total Capital to Risk-Weighted Assets (Amount)
Actual	$ 22,453	$ 23,534
Required Minimum Capital	$ 18,070	$ 19,402
Total Capital to Risk-Weighted Assets (Ratio)
Actual	0.130	0.127
Required Minimum Capital	0.105	0.105
Tier 1 Capital to Average Assets (Leverage) (Amount)
Actual	$ 19,411	$ 20,669
Required Minimum Capital	$ 8,759	$ 8,807
Tier 1 Capital to Average Assets (Leverage) (Ratio)
Actual	0.089	0.094
Required Minimum Capital	0.040	0.040
Capital conservation buffer	2.50%	2.50%