REGULATORY MATTERS - Capital and Capital Ratio Information (Details) $ in Millions	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Common Equity Tier 1 to Risk-Weighted Assets (Amount)
Actual	$ 14,607	$ 14,304
Minimum Capital Adequacy	$ 11,596	$ 10,004
Common Equity Tier 1 to Risk-Weighted Assets (Ratio)
Actual	0.100	0.100
Minimum Capital Adequacy	7.90%	7.00%
Tier 1 Capital to Risk-Weighted Assets (Amount)
Actual	$ 16,572	$ 15,874
Minimum Capital Adequacy	$ 13,797	$ 12,148
Tier 1 Capital to Risk-Weighted Assets (Ratio)
Actual	0.113	0.111
Minimum Capital Adequacy	0.094	0.085
Total Capital to Risk-Weighted Assets (Amount)
Actual	$ 19,602	$ 18,542
Minimum Capital Adequacy	$ 16,733	$ 15,006
Total Capital to Risk-Weighted Assets (Ratio)
Actual	0.134	0.130
Minimum Capital Adequacy	0.114	0.105
Tier 1 Capital to Average Assets (Leverage) (Amount)
Actual	$ 16,572	$ 15,874
Minimum Capital Adequacy	$ 7,015	$ 6,351
Tier 1 Capital to Average Assets (Leverage) (Ratio)
Actual	0.094	0.100
Minimum Capital Adequacy	0.040	0.040
Capital conservation buffer	3.40%	2.50%

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