Fair Value Measurements - Carrying Value and Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Estimate fair value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	$ 3,018.5	$ 1,494.3
Restricted cash, fair value	21.6	19.7
Notes payable, fair value	4,489.2	3,525.8
Cash and Cash Equivalents, carrying value	3,018.5	1,494.3
Restricted cash, carrying value	21.6	19.7
Notes payable, carrying value	4,283.3	3,399.4
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	3,018.5	1,494.3
Restricted cash, fair value	21.6	19.7
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	3,285.5	2,533.9
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	$ 1,203.7	$ 991.9

Amount 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

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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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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 equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, 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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