IMPAIRMENTS AND OTHER CHARGES - Summary of Impairments and Other Charges (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	May 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Impairments and other charges
Supply commitment charges		$ 3.2	$ 56.6
Employee severance costs		0.5
Impairment of assets			2.8
Inventory write-down			1.4
Total impairments and other charges		3.7	60.8
Reduction of commitments	$ 162.0
Liability for future severance payments		0.5
Estimated loss from commitments under contract			55.0
Proceeds from disposal of assets		$ 0.1	0.1
Discontinued Wireline Operations
Impairments and other charges
Inventory write-down			1.4
Impairment of assets			$ 2.8
Proceeds from disposal of assets				$ 3.7