Fair Value Measurements - Carrying Value and Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Estimate fair value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	$ 2,985.4	$ 4,516.4
Restricted cash, fair value	47.9	27.6
Notes payable, fair value	6,009.9	5,854.3
Cash and Cash Equivalents, carrying value	2,985.4	4,516.4
Restricted cash, carrying value	47.9	27.6
Notes payable, carrying value	5,965.5	5,917.7
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	2,985.4	4,516.4
Restricted cash, fair value	47.9	27.6
Notes payable, fair value	0.0	0.0
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	0.0	0.0
Restricted cash, fair value	0.0	0.0
Notes payable, fair value	3,811.1	3,413.7
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	0.0	0.0
Restricted cash, fair value	0.0	0.0
Notes payable, fair value	$ 2,198.8	$ 2,440.6

Amount of cash and cash equivalent. Cash includes, but is not limited to, currency on hand, demand deposit with financial institution, and account with general characteristic of demand deposit. Cash equivalent includes, but is not limited to, short-term, highly liquid investment that is both readily convertible to known amount of cash and so near maturity that it presents insignificant risk of change in value because of change in interest rate.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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Fair value portion of notes payable.

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Fair value portion of other assets.

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Amount of cash and cash equivalent restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposit with financial institution, and account with general characteristic of demand deposit. Cash equivalent includes, but is not limited to, short-term, highly liquid investment that is both readily convertible to known amount of cash and so near maturity that it presents insignificant risk of change in value because of change in interest rate.

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