ACCUMULATED OTHER COMPREHENSIVE LOSS - Roll-forward of Accumulated Other Comprehensive Loss (Details) - USD ($)		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		$ (1,862,000,000)	$ (1,221,200,000)
Foreign currency translation adjustment, net of tax		(8,700,000)	10,200,000
Amortization of pension related costs, net of tax	[1],[2]	13,800,000	11,400,000
Pension re-measurement, net of tax	[3]	38,100,000	(52,100,000)
Other comprehensive (loss) income, net	[4]	43,200,000	(30,500,000)
Ending balance		(2,014,100,000)	(1,862,000,000)
Pension re-measurement, tax expense (benefit)		300,000	(1,900,000)
Foreign currency translation adjustment, tax expense (benefit)		0	0
Amortization of pension related costs, tax expense (benefit)		0	0
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) income, net		43,200,000	(30,500,000)	[4]
Ending balance		(234,700,000)	(277,900,000)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(17,100,000)	(27,300,000)
Foreign currency translation adjustment, net of tax		(8,700,000)	10,200,000
Other comprehensive (loss) income, net		(8,700,000)	10,200,000
Ending balance		(25,800,000)	(17,100,000)
Actuarial (Loss) Gain on Post-retirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(260,500,000)	(219,800,000)
Amortization of pension related costs, net of tax		13,800,000	11,400,000
Pension re-measurement, net of tax		38,100,000	(52,100,000)
Other comprehensive (loss) income, net		51,900,000	(40,700,000)
Ending balance		(208,600,000)	(260,500,000)
Pension re-measurement, tax expense (benefit)		300,000	(1,900,000)
Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(300,000)	(300,000)
Other comprehensive (loss) income, net		0	0
Ending balance		$ (300,000)	$ (300,000)

[1] Net of tax benefit of nil for each of the years ended December 31, 2021 and 2020.

[2] This amount is included in the computation of net periodic benefit costs (income). See Note 11, "Pension and Post-Retirement Benefits," for additional information regarding net periodic benefit costs (income).

[3] Net of tax expense of $0.3 million and tax benefit of $1.9 million for the years ended December 31, 2021 and 2020, respectively.

[4] See Note 14, "Accumulated Other Comprehensive Loss," regarding the changes in the accumulated balances for each component of other comprehensive loss during the years ended December 31, 2021 and 2020, respectively.