PENSION PLANS AND OTHER POST-RETIREMENT BENEFITS - Narrative (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended		9 Months Ended	12 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 01, 2014	Sep. 30, 2014 Pension Plans	Dec. 31, 2013 Pension Plans	Dec. 31, 2012 Pension Plans	Sep. 30, 2014 Postretirement Plans	Dec. 31, 2013 Postretirement Plans	Dec. 31, 2012 Postretirement Plans	Sep. 30, 2014 Pension And Postretirement Cost	Dec. 31, 2013 Pension And Postretirement Cost
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Regulatory asset			$ 72.5	$ 67.8	$ 58.5		$ 4.7	$ 0		$ 0	$ 0.4
Regulatory liability			28.5	1.9	0		26.6	26.2
Settlement charge recognized for payment of lump sums from the nonqualified supplemental retirement plans	0	0.1		(10.1)	(1.4)	0
Settlements	0	0.5
Net periodic expense				16.8	26.6	16.4	(2.5)	0.2	3.6
Employer contributions				$ 1.6	$ 10.2		$ 0.3	$ 1.6