PENSION AND POST-RETIREMENT PLANS - ESTIMATED BENEFIT PAYMENTS (Details) $ in Millions	Dec. 31, 2017 USD ($)
Estimated future benefit payments
2018	$ 4.1
2019	4.1
2020	4.1
2021	4.1
2022	4.1
2023-2027	72.1
Total future payments	92.6
Pension Benefits
Estimated future benefit payments
2018	12.7
2019	13.0
2020	13.4
2021	13.7
2022	14.0
2023-2027	73.3
Total future payments	140.1
Other Post-retirement Benefits
Estimated future benefit payments
2018	1.2
2019	1.2
2020	1.2
2021	1.2
2022	1.2
2023-2027	7.0
Total future payments	13.0
Nonqualified Plan | Pension Benefits
Estimated future benefit payments
2018	1.8
2019	0.2
2020	0.5
2022	0.3
2023-2027	2.5
Total future payments	$ 5.3