PENSION AND POST-RETIREMENT PLANS - STATUS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Change in Benefit Obligation:
Benefit obligation at beginning of year	$ 217.4	$ 232.1
Service cost	4.7	4.4	$ 4.0
Interest cost	9.3	8.6	9.7
Actuarial (gain) loss	22.2	(14.1)
Benefits paid, net of subsidies received	(12.2)	(12.0)
Expenses paid	(1.5)	(1.6)
Benefit obligation at end of year	239.9	217.4	232.1
Change in Plan Assets:
Balance at the beginning of the period	162.2	186.7
Actual return on plan assets	36.3	(10.9)
Employer contribution	10.0	0.0	3.0
Benefits paid, net of subsidies received	(12.2)	(12.0)
Expenses paid	(1.5)	(1.6)
Balance at the end of the period	194.8	162.2	186.7
Funded Status and Recognized Liability	(45.1)	(55.2)
Post-retirement Benefits
Change in Benefit Obligation:
Benefit obligation at beginning of year	22.2	27.7
Service cost	0.4	0.6	0.5
Interest cost	0.9	1.0	1.1
Plan participants' contributions	0.8	0.9
Actuarial (gain) loss	3.4	(6.2)
Benefits paid, net of subsidies received	(1.7)	(1.8)
Benefit obligation at end of year	26.0	22.2	$ 27.7
Change in Plan Assets:
Plan participants' contributions	0.8	0.9
Employer contribution	0.9	0.9
Benefits paid, net of subsidies received	(1.7)	(1.8)
Funded Status and Recognized Liability	(26.0)	(22.2)
Qualified Plan | Pension Benefits
Change in Benefit Obligation:
Benefit obligation at beginning of year	215.9
Benefit obligation at end of year	238.3	215.9
Change in Plan Assets:
Balance at the beginning of the period	159.9
Balance at the end of the period	$ 192.2	$ 159.9