PENSION AND POST-RETIREMENT PLANS - STATUS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Change in Benefit Obligation:
Benefit obligation at beginning of year	$ 239.9	$ 217.4
Service cost	5.1	4.7	$ 4.4
Interest cost	7.9	9.3	8.6
Actuarial (gain) loss	23.9	22.2
Benefits paid, net of subsidies received	(12.5)	(12.2)
Expenses paid	(1.2)	(1.5)
Benefit obligation at end of year	263.1	239.9	217.4
Change in Plan Assets:
Balance at the beginning of the period	194.8	162.2
Actual return on plan assets	22.7	36.3
Employer contribution	9.0	10.0	0.0
Benefits paid, net of subsidies received	(12.5)	(12.2)
Expenses paid	(1.2)	(1.5)
Balance at the end of the period	212.8	194.8	162.2
Funded Status and Recognized Liability	(50.3)	(45.1)
Post-retirement Benefits
Change in Benefit Obligation:
Benefit obligation at beginning of year	26.0	22.2
Service cost	0.5	0.4	0.6
Interest cost	0.8	0.9	1.0
Plan participants' contributions	0.8	0.8
Actuarial (gain) loss	2.7	3.4
Benefits paid, net of subsidies received	(1.7)	(1.7)
Benefit obligation at end of year	29.1	26.0	$ 22.2
Change in Plan Assets:
Plan participants' contributions	0.8	0.8
Employer contribution	0.9	0.9
Benefits paid, net of subsidies received	(1.7)	(1.7)
Funded Status and Recognized Liability	(29.1)	(26.0)
Qualified Plan | Pension Benefits
Change in Benefit Obligation:
Benefit obligation at beginning of year	238.3
Benefit obligation at end of year	261.4	238.3
Change in Plan Assets:
Balance at the beginning of the period	192.2
Balance at the end of the period	$ 210.0	$ 192.2