EMPLOYEE BENEFITS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Components of net periodic benefit cost
Contributions and payments related to pension and OPEB plans			$ 115.4	$ 23.5
Pension Costs
Components of net periodic benefit cost
Service cost	$ 11.1	$ 10.9	33.2	32.9
Interest cost	30.3	33.2	91.7	99.4
Expected return on plan assets	(48.8)	(49.0)	(146.9)	(147.0)
Loss on plan settlement	2.9	0.7	8.2	14.8
Amortization of prior service cost (credit)	0.7	0.9	2.2	2.6
Amortization of net actuarial loss	21.5	20.4	64.5	61.1
Net periodic benefit (credit) cost	17.7	17.1	52.9	63.8
Contributions and payments related to pension and OPEB plans			109.8
Estimated future employer contributions for the remainder of the year	3.8		3.8
Other Postretirement Benefit Costs
Components of net periodic benefit cost
Service cost	6.0	6.5	17.9	19.6
Interest cost	8.4	9.2	25.3	27.7
Expected return on plan assets	(13.6)	(13.2)	(40.9)	(39.6)
Amortization of prior service cost (credit)	(2.8)	(2.3)	(8.4)	(7.0)
Amortization of net actuarial loss	0.7	2.2	2.3	6.4
Net periodic benefit (credit) cost	(1.3)	$ 2.4	(3.8)	$ 7.1
Contributions and payments related to pension and OPEB plans			5.6
Estimated future employer contributions for the remainder of the year	$ 3.9		$ 3.9