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LOAN PORTFOLIO - Narratives (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Accounts Notes And Loans Receivable [Line Items]      
Additional interest income that would have realized $ 35.2 $ 43.2 $ 37.8
Mortgages pledged as collateral 1,900.0 2,000.0  
Origination Fees [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Loans And Leases Receivable Deferred Income 4.0 4.8  
Unearned Income [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Loans And Leases Receivable Deferred Income 38.6 32.8  
Residential Mortgage [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Servicing of loans 2,800.0 2,700.0  
Commercial loan [Member]      
Accounts Notes And Loans Receivable [Line Items]      
Servicing of loans $ 361.3 $ 401.4