REGULATORY MATTERS - Capital and Capital Ratio Information (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Common Equity Tier 1 to Risk-Weighted Assets (Amount)
Actual	[1]	$ 14,435	$ 14,309
Minimum Capital Adequacy	[1]	$ 8,495	$ 7,342
Common Equity Tier 1 to Risk-Weighted Assets (Ratio)
Actual	[1]	10.80%	11.20%
Common Equity Tier1 Required For Capital Adequacy To Risk Weighted Assets	[1],[2]	6.375%	5.75%
Tier 1 Capital to Risk-Weighted Assets (Amount)
Actual	[3]	$ 14,978	$ 14,556
Minimum Capital Adequacy	[3]	$ 10,493	$ 9,258
Tier 1 Capital to Risk-Weighted Assets (Ratio)
Actual	[3]	11.20%	11.40%
Minimum Capital Adequacy	[2],[3]	7.875%	7.25%
Total Capital to Risk-Weighted Assets (Amount)
Actual	[4]	$ 17,810	$ 17,781
Minimum Capital Adequacy	[4]	$ 13,158	$ 11,812
Total Capital to Risk-Weighted Assets (Ratio)
Actual	[4]	13.40%	13.90%
Minimum Capital Adequacy	[2],[4]	9.875%	9.25%
Tier 1 Capital to Average Assets (Leverage) (Amount)
Actual	[5]	$ 14,978	$ 14,556
Minimum Capital Adequacy	[5]	$ 6,029	$ 5,824
Tier 1 Capital to Average Assets (Leverage) (Ratio)
Actual	[5]	9.90%	10.00%
Minimum Capital Adequacy	[2],[5]	4.00%	4.00%
Capital Conservation Buffer		1.875%	1.25%

[1] “Common equity tier 1 capital ratio” represents CET1 capital divided by total risk-weighted assets as defined under U.S. Basel III Standardized approach.

[2] “Minimum Capital ratio” includes capital conservation buffer of 1.875% for 2018 and 1.250% for 2017; N/A to Tier 1 leverage.

[3] “Tier 1 capital ratio” is tier 1 capital, which includes CET1 capital plus non-cumulative perpetual preferred equity that qualifies as additional tier 1 capital, divided by total risk-weighted assets as defined under U.S. Basel III Standardized approach.

[4] “Total capital ratio” is total capital divided by total risk-weighted assets as defined under U.S. Basel III Standardized approach.

[5] “Tier 1 leverage ratio” is tier 1 capital divided by quarterly average total assets as defined under U.S. Basel III Standardized approach.