EMPLOYEE BENEFIT PLANS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension Benefits
Components of net periodic benefit cost (including amounts capitalized to the balance sheets)
Service cost	$ 7.1	$ 5.9	$ 14.7	$ 12.5
Interest cost	16.7	19.3	33.7	39.0
Expected return on plan assets	(25.8)	(28.5)	(52.7)	(57.4)
Loss on plan settlement	0.7	0.9	1.2	0.9
Amortization of prior service cost (credit)	0.0	0.1	0.1	0.3
Amortization of net actuarial loss	12.1	8.6	22.6	17.0
Net periodic benefit cost	10.8	6.3	19.6	12.3
Other Postretirement Benefits
Components of net periodic benefit cost (including amounts capitalized to the balance sheets)
Service cost	5.4	4.8	11.2	10.7
Interest cost	5.1	5.2	10.4	12.3
Expected return on plan assets	(7.9)	(7.9)	(15.8)	(16.7)
Loss on plan settlement	0.0	0.0	0.0	0.0
Amortization of prior service cost (credit)	(2.5)	(2.8)	(5.1)	(4.1)
Amortization of net actuarial loss	0.8	0.8	1.9	1.5
Net periodic benefit cost	$ 0.9	$ 0.1	$ 2.6	$ 3.7