DEFERRED REVENUE - Schedule of Performance Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 76.0	$ 75.7
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 67.0
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Less than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 22.5
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Greater than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 44.5
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 38.9
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Less than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 0.0
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Greater than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 38.9
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 36.8
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Less than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 0.0
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Greater than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 36.8
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 35.0
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Less than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 0.0
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Greater than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 35.0
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 28.0
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Less than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 0.0
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Greater than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 28.0
Performance obligation period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 127.8
Performance obligation period
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Less than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 0.0
Performance obligation period
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01 | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Greater than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 127.8
Performance obligation period
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil) | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 333.5
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil) | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Less than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	22.5
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil) | Prepaid Services, IRUs, And Deferred Non-Recurring Revenue | Greater than 1 Year
Deferred Revenue Arrangement [Line Items]
Performance obligations	$ 311.0