v3.26.1
Notes Payable - Principal Amounts (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Sep. 30, 2025
Estimate of Fair Value Measurement [Member]    
Debt Instrument [Line Items]    
Notes payable, Fair value $ 7,100.0 $ 6,000.0
Notes payable 7,112.6 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 3,300.0 2,200.0
HomeBuildingOps    
Debt Instrument [Line Items]    
Revolving credit facility 500.0 0.0
Notes payable 3,685.3 3,154.4
Other Notes Payable 208.0 180.6
Unamortized Debt Issuance Expense 16.3 18.9
Rental    
Debt Instrument [Line Items]    
Revolving credit facility 820.0 600.0
Notes payable 820.3 600.0
Other Notes Payable 0.3 0.0
Forestar Group [Member]    
Debt Instrument [Line Items]    
Revolving credit facility 0.0 0.0
Notes payable 793.8 802.8
Other Notes Payable 0.0 9.9
Unamortized Debt Issuance Expense 6.2 7.2
Financial Services [Member]    
Debt Instrument [Line Items]    
Notes payable 1,813.2 1,408.3
1.3% Senior Notes due 2026 [Member] | HomeBuildingOps    
Debt Instrument [Line Items]    
Notes payable $ 599.7 598.8
Debt Instrument, Interest Rate, Stated Percentage 1.30%  
1.4% Senior Notes due 2027 [Member] | HomeBuildingOps    
Debt Instrument [Line Items]    
Notes payable $ 498.9 498.2
Debt Instrument, Interest Rate, Stated Percentage 1.40%  
4.85% Senior Notes due 2030 | HomeBuildingOps    
Debt Instrument [Line Items]    
Notes payable $ 496.1 495.5
Debt Instrument, Interest Rate, Stated Percentage 4.85%  
5.0% Senior Notes due 2034 [Member] | HomeBuildingOps    
Debt Instrument [Line Items]    
Notes payable $ 688.6 687.7
Debt Instrument, Interest Rate, Stated Percentage 5.00%  
5.5% Senior Notes due 2035 [Member] | HomeBuildingOps    
Debt Instrument [Line Items]    
Notes payable $ 694.0 693.6
Debt Instrument, Interest Rate, Stated Percentage 5.50%  
5.0% Senior Notes due 2028 [Member] | Forestar Group [Member]    
Debt Instrument [Line Items]    
Notes payable $ 299.1 298.7
Debt Instrument, Interest Rate, Stated Percentage 5.00%  
6.5% Senior Notes due 2033 [Member] | Forestar Group [Member]    
Debt Instrument [Line Items]    
Notes payable $ 494.7 494.2
Debt Instrument, Interest Rate, Stated Percentage 6.50%  
Commitments to Extend Credit [Member] | Financial Services [Member]    
Debt Instrument [Line Items]    
Notes payable $ 1,512.1 1,103.5
Warehouse Agreement Borrowings [Member] | Financial Services [Member]    
Debt Instrument [Line Items]    
Notes payable $ 301.1 $ 304.8