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CAPITAL CONSTRUCTION FUND (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Maximum period to commit fund deposits for qualified purposes 25 years  
Period over which deposits will be treated as non-qualified withdrawals 5 years  
Accounts receivable, net $ 214.3 $ 197.6
Capital Construction Fund - cash on deposit   27.5
Eligible Accounts Receivable Assigned to CCF    
Accounts receivable, net $ 176.6 150.7
CCF Cash Deposits and Withdrawals | Long-term Assets    
Capital Construction Fund - cash on deposit   $ 27.5