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PENSION AND POST-RETIREMENT PLANS - FAIR VALUE (Details) - Pension Benefits - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension and Post-retirement Plans
Total	$ 212.8	$ 194.8	$ 162.2
Fair Value Measurement
Pension and Post-retirement Plans
Total	170.9	157.3
Total plan assets	212.8	194.8
Fair Value Measurement | Cash
Pension and Post-retirement Plans
Total	3.8	6.3
Fair Value Measurement | U.S. large-cap
Pension and Post-retirement Plans
Total	71.3	62.4
Fair Value Measurement | U.S. mid- and small-cap
Pension and Post-retirement Plans
Total	54.3	49.6
Fair Value Measurement | International large-cap
Pension and Post-retirement Plans
Total	7.0	6.6
Fair Value Measurement | U.S. Treasuries
Pension and Post-retirement Plans
Total	12.0	14.1
Fair Value Measurement | Investment grade U.S. corporate bonds
Pension and Post-retirement Plans
Total	22.5	18.2
Fair Value Measurement | High-yield U.S. corporate bonds
Pension and Post-retirement Plans
Total		0.1
Fair Value Measurement | Quoted Prices in Active Markets (Level 1)
Pension and Post-retirement Plans
Total	68.9	63.9
Fair Value Measurement | Quoted Prices in Active Markets (Level 1) | Cash
Pension and Post-retirement Plans
Total	3.8	6.3
Fair Value Measurement | Quoted Prices in Active Markets (Level 1) | U.S. large-cap
Pension and Post-retirement Plans
Total	28.9	23.7
Fair Value Measurement | Quoted Prices in Active Markets (Level 1) | U.S. mid- and small-cap
Pension and Post-retirement Plans
Total	36.2	33.9
Fair Value Measurement | Significant Observable Inputs (Level 2)
Pension and Post-retirement Plans
Total	102.0	93.4
Fair Value Measurement | Significant Observable Inputs (Level 2) | U.S. large-cap
Pension and Post-retirement Plans
Total	42.4	38.7
Fair Value Measurement | Significant Observable Inputs (Level 2) | U.S. mid- and small-cap
Pension and Post-retirement Plans
Total	18.1	15.7
Fair Value Measurement | Significant Observable Inputs (Level 2) | International large-cap
Pension and Post-retirement Plans
Total	7.0	6.6
Fair Value Measurement | Significant Observable Inputs (Level 2) | U.S. Treasuries
Pension and Post-retirement Plans
Total	12.0	14.1
Fair Value Measurement | Significant Observable Inputs (Level 2) | Investment grade U.S. corporate bonds
Pension and Post-retirement Plans
Total	22.5	18.2
Fair Value Measurement | Significant Observable Inputs (Level 2) | High-yield U.S. corporate bonds
Pension and Post-retirement Plans
Total		0.1
Fair Value Measurement | Investment measured at NAV
Pension and Post-retirement Plans
Total	$ 41.9	$ 37.5

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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