PENSION AND OTHER POST-EMPLOYMENT BENEFITS - Fair Value of Pension Plan Investments (Details) - Pension Benefits - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	$ 181.7	$ 233.9	$ 273.9
Level 1
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	4.6	7.5
Level 1 | Short-term investments
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	4.6	7.5
Level 1 | U.S. government securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0.0	0.0
Level 1 | Corporate bonds
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0.0	0.0
Level 1 | Certificates of deposit
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments		0.0
Level 1 | Asset-backed securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments		0.0
Level 2
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	77.7	114.1
Level 2 | Short-term investments
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0.0	0.0
Level 2 | U.S. government securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	19.8	37.2
Level 2 | Corporate bonds
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	57.9	71.6
Level 2 | Certificates of deposit
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments		1.5
Level 2 | Asset-backed securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments		3.8
Level 3
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0.0	0.0
Level 3 | Short-term investments
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0.0	0.0
Level 3 | U.S. government securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0.0	0.0
Level 3 | Corporate bonds
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	0.0	0.0
Level 3 | Certificates of deposit
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments		0.0
Level 3 | Asset-backed securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments		0.0
Fair Value, Inputs, Level 1, 2 and 3
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	82.3	121.6
Fair Value, Inputs, Level 1, 2 and 3 | Short-term investments
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	4.6	7.5
Fair Value, Inputs, Level 1, 2 and 3 | U.S. government securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	19.8	37.2
Fair Value, Inputs, Level 1, 2 and 3 | Corporate bonds
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	57.9	71.6
Fair Value, Inputs, Level 1, 2 and 3 | Certificates of deposit
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments		1.5
Fair Value, Inputs, Level 1, 2 and 3 | Asset-backed securities
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments		3.8
Investments measured at net asset value
PENSIONS AND OTHER POSTRETIREMENT BENEFITS
Fair value of pension plan investments	$ 99.4	$ 112.3