Capitalized Interest Capitalized Interest (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Real Estate Inventory, Capitalized Interest Costs [Roll Forward]
Capitalized interest, beginning of year	$ 180.1	$ 162.7	$ 167.9
Interest incurred	153.3	140.2	125.4
Charged to cost of sales	(125.7)	(122.8)	(130.6)
Capitalized interest, end of year	207.7	180.1	162.7
Financial Services [Member]
Real Estate Inventory, Capitalized Interest Costs [Roll Forward]
Interest incurred	19.1	16.1	12.1
Forestar Group [Member]
Real Estate Inventory, Capitalized Interest Costs [Roll Forward]
Interest incurred	$ 41.2	$ 19.4	$ 3.4

Total interest costs incurred during the period and either capitalized or charged against earnings.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

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- Definition

Carrying amount as of the balance sheet date of interest costs that were capitalized to properties under development during the land development and construction period of a project, and which are included in inventory.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

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Amount of interest cost charged to cost of sales that had been previously capitalized to inventory.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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