CAPITAL CONSTRUCTION FUND (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	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
Cash Deposits Into CCF	$ 123.4	$ 77.9	$ 31.9
Accounts receivable, net	189.5	192.8
Eligible Accounts Receivable Assigned to CCF
Accounts receivable, net	174.7	176.6
Cash | Long-term Assets
Capital Construction Fund - cash on deposit	$ 31.2	$ 31.2