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SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION - Deferred Revenue (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019
Revenue Recognition, Multiple-deliverable Arrangements [Line Items] |  |  |  |
Realization of deferred revenue | $ 0.0 | $ 0.0 | $ 34.6 | $ 0.0
Other Current Liabilities [Member] |  |  |  |
Revenue Recognition, Multiple-deliverable Arrangements [Line Items] |  |  |  |
Opening balance as of January 1 |  |  | 22.1 | 21.0
Contract With Customer, Liability, Period Increase (Decrease) |  |  | (17.2) | (5.5)
Closing balance as of June 30 | 4.9 | 15.5 | 4.9 | 15.5
Other Noncurrent Liabilities [Member] |  |  |  |
Revenue Recognition, Multiple-deliverable Arrangements [Line Items] |  |  |  |
Opening balance as of January 1 |  |  | 25.7 | 38.5
Contract With Customer, Liability, Period Increase (Decrease) |  |  | (25.7) | (4.2)
Closing balance as of June 30 | $ 0.0 | $ 34.3 | $ 0.0 | $ 34.3

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