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Real Estate - Text (Detail) - USD ($) $ in Millions	12 Months Ended
Real Estate - Text (Detail) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Real Estate Properties [Line Items]
Real estate	$ 2,266.2	$ 1,790.3
Payments to Acquire Residential Real Estate	570.0
Payments to Develop Real Estate Assets	1,000.0
Asset Impairment Charges	0.0	19.4	$ 3.8
Loss on Contract Termination	4.1	4.6	$ 8.7
Developed and under development projects
Real Estate Properties [Line Items]
Real estate	2,126.1	1,760.8
Land held for future development
Real Estate Properties [Line Items]
Real estate	$ 140.1	$ 29.5
D.R. Horton, Inc. [Member] \| Minimum
Real Estate Properties [Line Items]
Related Party Transaction, Rate	12.00%
D.R. Horton, Inc. [Member] \| Maximum
Real Estate Properties [Line Items]
Related Party Transaction, Rate	16.00%