REGULATORY CAPITAL REQUIREMENTS - Narratives (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Regulatory capital requirements
Capital conversion buffer - 2016	0.625%
Increase in capital conversion buffer each year ( as a percent)	0.625%
Capital conservation buffer - 2019	2.50%
Actual, Ratio (as a percent)	7.00%
Actual, Ratio (as a percent)	8.50%
Actual, Ratio (as a percent)	10.50%
Basel III
Regulatory capital requirements
Additional capital conservation buffer (as a percentage)	2.50%
Actual, Ratio (as a percent)	10.40%	10.00%
Actual, Ratio (as a percent)	10.40%	10.00%
Actual, Ratio (as a percent)	13.60%	13.30%