Fair Value Measurements and Derivative Instruments - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($) $ in Millions	Sep. 30, 2022	Sep. 30, 2021
Carrying Value | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	$ 13.6	$ 14.7
Carrying Value | Other Assets | Interest Rate Swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	3.0
Carrying Value | Other Assets | Fuel Swap Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets		1.2
Carrying Value | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	10.6	17.1
Carrying Value | Other Liabilities | Interest Rate Swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities		3.6
Investment Held by Rabbi Trust | Carrying Value | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	10.6	13.5
Investment Held by Rabbi Trust | Carrying Value | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	10.6	13.5
Level 1 | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	10.6	13.5
Level 1 | Other Assets | Interest Rate Swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	0.0
Level 1 | Other Assets | Fuel Swap Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets		0.0
Level 1 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	10.6	13.5
Level 1 | Other Liabilities | Interest Rate Swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities		0.0
Level 1 | Investment Held by Rabbi Trust | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	10.6	13.5
Level 1 | Investment Held by Rabbi Trust | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	10.6	13.5
Level 2 | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	3.0	1.2
Level 2 | Other Assets | Interest Rate Swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	3.0
Level 2 | Other Assets | Fuel Swap Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets		1.2
Level 2 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	0.0	3.6
Level 2 | Other Liabilities | Interest Rate Swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities		3.6
Level 2 | Investment Held by Rabbi Trust | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	0.0	0.0
Level 2 | Investment Held by Rabbi Trust | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	0.0	0.0
Level 3 | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	0.0	0.0
Level 3 | Other Assets | Interest Rate Swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	0.0
Level 3 | Other Assets | Fuel Swap Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets		0.0
Level 3 | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	0.0	0.0
Level 3 | Other Liabilities | Interest Rate Swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities		0.0
Level 3 | Investment Held by Rabbi Trust | Other Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Assets	0.0	0.0
Level 3 | Investment Held by Rabbi Trust | Other Liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total Liabilities	$ 0.0	$ 0.0