STOCK-BASED COMPENSATION PLANS - Unrecognized Stock-Based Compensation Expense and Stock Option Exercises (Details) - Stock Options [Member] - USD ($) shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unrecognized Stock-Based Compensation Expense and Stock Option Exercises
Unrecognized stock-based compensation expense related to non-vested stock options	$ 5.0
Weighted average period for recognition of unrecognized compensation cost	3 years 2 months 12 days
Total fair value of stock options vested	$ 2.5	$ 2.4	$ 2.3
Proceeds from stock option exercises	7.5	11.3
Related tax benefits from stock option exercises	$ 1.2	$ 2.3
Shares issued in connection with stock option exercise (in shares)	0.2	0.3
Total intrinsic value of options exercised	$ 6.6	$ 11.6	$ 8.4

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for option under share-based payment arrangement.

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Amount of tax benefit from exercise of option under share-based payment arrangement.

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Number of shares issued under share-based payment arrangement.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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