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Fair Value Measurements and Derivative Instruments - Summary of Effects on Consolidated Financial Statements of Designated As Cash Flow Hedges (Details) - Cash Flow Hedges - Designated - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Interest Rate Swaps |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Income (loss) recognized in Other comprehensive income (loss) | $ (0.2) | $ (2.2) | $ (0.3) | $ (10.2)
Interest Rate Swaps | Interest Expense |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Net (loss) income reclassified from Accumulated other comprehensive Income (loss) into Interest expense/Cost of services provided | (0.8) | (4.9) | (6.1) | (11.6)
Fuel Swap Contracts |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Income (loss) recognized in Other comprehensive income (loss) | 1.2 | 1.5 | 3.2 | (3.9)
Fuel Swap Contracts | Cost of Services Provided |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Net (loss) income reclassified from Accumulated other comprehensive Income (loss) into Interest expense/Cost of services provided | $ 1.2 | $ (1.7) | $ 0.8 | $ (1.5)

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