BORROWED FUNDS - Short Term Borrowed Debt Key Data (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Federal funds purchased and securities sold under agreements to repurchase
Short-term Debt [Line Items]
Weighted-average interest rate at period end	0.14%	0.09%	0.10%
Maximum amount outstanding at month-end during the period	$ 7,022	$ 5,114	$ 4,393
Average amount outstanding during the period	5,699	2,400	2,716
Weighted-average interest rate during the period	0.12%	0.31%	0.22%
Other short-term borrowed funds
Short-term Debt [Line Items]
Weighted-average interest rate at period end	0.26%	0.20%	0.29%
Maximum amount outstanding at month-end during the period	7,702	2,251	5,050
Average amount outstanding during the period	$ 5,640	$ 251	$ 3,026
Weighted-average interest rate during the period	0.25%	0.44%	0.33%