PENSION AND OTHER SAVING PLANS - Multiemployer Plans (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) $ / Hour	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jan. 31, 2012
Multiemployer Plans [Line Items]
Multiemployer Plans Funded Status Minimum Percentage				80.00%
WECO [Member]
Multiemployer Plans [Line Items]
Multiemployer Plan Minimum Contribution Per Hour Worked	5.85
Multiemployer Plan Maximum Contribution Per Hour Worked	5.90
Multiemployer Plan, Period Contributions | $	$ 3.7	$ 3.6	$ 3.3
WRI [Member]
Multiemployer Plans [Line Items]
Multiemployer Plan Minimum Contribution Per Hour Worked	4.03
Multiemployer Plan Maximum Contribution Per Hour Worked	4.39
Multiemployer Plan, Period Contributions | $	$ 0.8	1.1	1.2
WSC [Member]
Multiemployer Plans [Line Items]
Multiemployer Plan Minimum Contribution Per Hour Worked	3.70
Multiemployer Plan, Period Contributions | $	$ 0.1	$ 0.1	$ 0.1