CAPITAL CONSTRUCTION FUND (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Eligible Accounts Receivable Assigned to CCF
Balance	$ 151.1	$ 151.1	$ 150.9	$ 150.7
Interest earned	0.2	0.4
CCF Deposits and Withdrawals
Balance	27.5	27.5	27.5	27.5
Deposits		2.2
Qualified withdrawals		(2.2)
CAPITAL CONSTRUCTION FUND Total
Balance	178.6	178.6	$ 178.4	$ 178.2
Deposits		2.2
Qualified withdrawals		(2.2)
Interest earned	$ 0.2	$ 0.4