v3.26.1
Notes Payable - Principal Amounts (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Sep. 30, 2025
Estimate of Fair Value Measurement [Member]    
Debt Instrument [Line Items]    
Notes payable, Fair value $ 6,600.0 $ 6,000.0
Notes payable 6,563.8 5,965.5
Fair Value, Inputs, Level 2 [Member]    
Debt Instrument [Line Items]    
Notes payable, Fair value 3,800.0 3,800.0
Fair Value, Inputs, Level 3 [Member]    
Debt Instrument [Line Items]    
Notes payable, Fair value 2,800.0 2,200.0
HomeBuildingOps    
Debt Instrument [Line Items]    
Revolving credit facility 250.0 0.0
Notes payable 3,427.1 3,154.4
Unamortized Debt Issuance Expense 17.2 18.9
HomeBuildingOps | Unsecured Debt    
Debt Instrument [Line Items]    
Notes payable 201.1 180.6
Rental    
Debt Instrument [Line Items]    
Revolving credit facility 865.0 600.0
Notes payable 865.0 600.0
Financial Services [Member]    
Debt Instrument [Line Items]    
Notes payable 1,478.2 1,408.3
Forestar Group [Member]    
Debt Instrument [Line Items]    
Revolving credit facility 0.0 0.0
Notes payable 793.5 802.8
Unamortized Debt Issuance Expense 6.5 7.2
Forestar Group [Member] | Secured Debt    
Debt Instrument [Line Items]    
Notes payable 0.0 9.9
1.3% Senior Notes due 2026 [Member] | HomeBuildingOps    
Debt Instrument [Line Items]    
Notes payable $ 599.4 598.8
Debt Instrument, Interest Rate, Stated Percentage 1.30%  
1.4% Senior Notes due 2027 [Member] | HomeBuildingOps    
Debt Instrument [Line Items]    
Notes payable $ 498.6 498.2
Debt Instrument, Interest Rate, Stated Percentage 1.40%  
4.85% Senior Notes due 2030 | HomeBuildingOps    
Debt Instrument [Line Items]    
Notes payable $ 495.9 495.5
Debt Instrument, Interest Rate, Stated Percentage 4.85%  
5.0% Senior Notes due 2034 [Member] | HomeBuildingOps    
Debt Instrument [Line Items]    
Notes payable $ 688.3 687.7
Debt Instrument, Interest Rate, Stated Percentage 5.00%  
5.5% Senior Notes due 2035 [Member] | HomeBuildingOps    
Debt Instrument [Line Items]    
Notes payable $ 693.8 693.6
Debt Instrument, Interest Rate, Stated Percentage 5.50%  
5.0% Senior Notes due 2028 [Member] | Forestar Group [Member]    
Debt Instrument [Line Items]    
Notes payable $ 298.9 298.7
Debt Instrument, Interest Rate, Stated Percentage 5.00%  
6.5% Senior Notes due 2033 [Member] | Forestar Group [Member]    
Debt Instrument [Line Items]    
Notes payable $ 494.6 494.2
Debt Instrument, Interest Rate, Stated Percentage 6.50%  
Commitments to Extend Credit [Member] | Financial Services [Member]    
Debt Instrument [Line Items]    
Notes payable $ 1,062.1 1,103.5
Warehouse Agreement Borrowings [Member] | Financial Services [Member]    
Debt Instrument [Line Items]    
Notes payable $ 416.1 $ 304.8