EMPLOYEE BENEFITS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Employee Benefit Plans
Document Fiscal Year Focus	2017
Components of net periodic benefit costs
Contributions and payments related to pension and OPEB plans	$ 3.3	$ 2.9
Pension Costs
Components of net periodic benefit costs
Service cost	3.0	2.7
Interest cost	11.9	12.6
Expected return on plan assets	(19.2)	(19.4)
Amortization of prior service cost (credit)	0.3	0.4
Amortization of net actuarial loss	8.8	8.0
Net periodic benefit cost	4.8	4.3
Contributions and payments related to pension and OPEB plans	2.6
Estimated future employer contributions for the remainder of the year	2.3
Other Postretirement Benefit Costs
Components of net periodic benefit costs
Service cost	1.9	0.1
Interest cost	3.1	1.9
Expected return on plan assets	(3.6)	(1.2)
Amortization of prior service cost (credit)	(0.3)	(0.3)
Amortization of net actuarial loss	0.3	0.2
Net periodic benefit cost	1.4	$ 0.7
Contributions and payments related to pension and OPEB plans	0.7
Estimated future employer contributions for the remainder of the year	$ 3.7