Quarterly report pursuant to Section 13 or 15(d)

COMMITMENTS AND CONTINGENT LIABILITIES - Narrative (Details)

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COMMITMENTS AND CONTINGENT LIABILITIES - Narrative (Details)
 3 Months Ended 12 Months Ended
Mar. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Sep. 30, 2015
USD ($)
Dec. 31, 2010
lawsuit
Sep. 28, 2015
USD ($)
Loss Contingencies [Line Items]          
Maturity period of majority of standby letters of credit P2Y        
Maturity period of Commercial letters of credit P90D        
Maturity period of forward contracts relating mortgage banking business 1 year        
Cyberco Litigation          
Loss Contingencies [Line Items]          
Bankruptcy Court recommended judgment amount in Cyberco case, principal         $ 72,000,000
Loss contingency period increase (decrease)   $ (42,000,000) $ 38,000,000    
FirstMerit Merger Litigation          
Loss Contingencies [Line Items]          
Number of lawsuits | lawsuit       2  
Standby Letters of Credit          
Loss Contingencies [Line Items]          
Carrying amount of deferred revenue associated with guarantees $ 7,000,000 8,000,000      
Outstanding standby letters of credit 560,718,000 637,182,000      
Commercial letters-of-credit          
Loss Contingencies [Line Items]          
Outstanding standby letters of credit 5,160,000 4,610,000      
Commitments to Sell Loans          
Loss Contingencies [Line Items]          
Commitments to sell residential real estate loans 900,000,000 819,000,000      
Maximum          
Loss Contingencies [Line Items]          
Aggregate range of reasonably possible losses current legal proceedings 70,000,000        
Minimum          
Loss Contingencies [Line Items]          
Aggregate range of reasonably possible losses current legal proceedings $ 0        
Cash [Member] | FirstMerit Overdraft Litigation [Member]          
Loss Contingencies [Line Items]          
Litigation Settlement, Amount   9,000,000      
Debt forgiveness [Member] | FirstMerit Overdraft Litigation [Member]          
Loss Contingencies [Line Items]          
Litigation Settlement, Amount   7,000,000      
Insurance Settlement [Member] | FirstMerit Overdraft Litigation [Member]          
Loss Contingencies [Line Items]          
Litigation Settlement, Amount   $ 4,400,000