PENSION AND POST-RETIREMENT PLANS - STATUS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Qualified Pension Benefits
Change in Benefit Obligation:
Benefit obligation at beginning of year	$ 237.4	$ 197.5
Service cost	3.3	3.3	$ 2.9
Interest cost	9.5	9.4	8.6
Actuarial (gain) loss	(17.9)	38.2
Benefits paid, net of subsidies received	(10.9)	(10.0)
Expenses paid	(1.2)	(1.0)
Benefit obligation at end of year	220.2	237.4	197.5
Changes in plan assets:
Balance at the beginning of the period	178.9	172.8
Actual return on plan assets	(2.6)	10.6
Employer contribution	4.7	6.5	3.5
Benefits paid, net of subsidies received	(10.9)	(10.0)
Expenses paid	(1.2)	(1.0)
Balance at the end of the period	168.9	178.9	172.8
Funded Status and Recognized Liability	(51.3)	(58.5)
Post-retirement Benefits
Change in Benefit Obligation:
Benefit obligation at beginning of year	62.6	52.1
Service cost	1.5	1.1
Interest cost	2.5	2.6
Plan participants' contributions	0.9	0.7
Actuarial (gain) loss	(3.1)	9.7
Benefits paid, net of subsidies received	(3.9)	(3.6)
Benefit obligation at end of year	60.5	62.6	$ 52.1
Changes in plan assets:
Plan participants' contributions	0.9	0.7
Employer contribution	3.0	2.9
Benefits paid, net of subsidies received	(3.9)	(3.6)
Funded Status and Recognized Liability	$ (60.5)	$ (62.6)