Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The amount of inventory recognized as of the acquisition date.

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Amount recognized as of the acquisition date for the assets, including goodwill, in excess of (less than) the aggregate liabilities assumed, less the noncontrolling interest in the acquiree.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Business Acquisitions (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Payments related to business acquisitions, net of cash acquired		$ (315.8)	$ (159.2)	$ (4.1)
Goodwill		163.5	109.2
Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition [Line Items]
Payments related to business acquisitions, net of cash acquired	$ (325.9)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory	265.5
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets	23.3
Goodwill	54.3
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	8.6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	(25.8)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest	325.9
Home Building [Member]
Business Acquisition [Line Items]
Goodwill		$ 134.3	80.0
Maximum [Member] \| Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		3 years
Midwest [Member] \| Home Building [Member]
Business Acquisition [Line Items]
Goodwill	49.7	$ 49.7	0.0
East [Member] \| Home Building [Member]
Business Acquisition [Line Items]
Goodwill	$ 4.6	$ 26.4	$ 21.8