ACCUMULATED OTHER COMPREHENSIVE LOSS - Roll-forward of Accumulated Other Comprehensive Loss (Details) - USD ($)		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		$ (1,862,000,000.0)	$ (1,221,200,000)
Foreign currency translation adjustment, net of tax		(4,900,000)	(5,200,000)
Amortization of pension related costs, net of tax	[1],[2]	3,500,000	2,500,000
Other comprehensive loss, net	[3]	(1,400,000)	(2,700,000)
Ending balance		(1,958,700,000)	(1,435,800,000)
Amortization of pension related costs, tax expense		0	(300,000)
Accumulated Other Comprehensive (Loss) Income
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(277,900,000)	(247,400,000)
Other comprehensive loss, net	[3]	(1,400,000)	(2,700,000)
Ending balance		(279,300,000)	$ (250,100,000)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(17,100,000)
Foreign currency translation adjustment, net of tax		(4,900,000)
Other comprehensive loss, net		(4,900,000)
Ending balance		(22,000,000.0)
Foreign currency translation adjustment, tax expense		0
Actuarial (Loss) Gain on Post-retirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(260,500,000)
Amortization of pension related costs, net of tax		3,500,000
Other comprehensive loss, net		3,500,000
Ending balance		(257,000,000.0)
Amortization of pension related costs, tax expense		0
Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(300,000)
Other comprehensive loss, net		0
Ending balance		$ (300,000)

[1] Net of tax expense of nil and $0.3 million for the three months ended March 31, 2021 and 2020, respectively.

[2] This amount is included in the computation of net periodic benefit costs (income). See Note 10, "Pension and Post-Retirement Benefits," for additional information regarding net periodic benefit costs (income).

[3] See Note 13, "Accumulated Other Comprehensive Loss," regarding the changes in the accumulated balances for each component of other comprehensive loss during the three months ended March 31, 2021 and 2020, respectively.