Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share Reconciliation [Abstract]
Net Income (Loss) Attributable to Parent	$ 466.1	$ 453.8	$ 351.0	$ 189.3	$ 313.2	$ 289.0	$ 229.2	$ 206.9	$ 1,460.3	$ 1,038.4	$ 886.3
Denominator:
Denominator for basic earnings per share - weighted average common shares									376.6	374.3	371.0
Effect of dilutive securities:
Employee stock awards									6.8	4.6	4.1
Denominator for diluted earnings per share - adjusted weighted average common shares									383.4	378.9	375.1
Basic net income per common share attributable to D.R. Horton, Inc.	$ 1.24	$ 1.20	$ 0.93	$ 0.50	$ 0.84	$ 0.77	$ 0.61	$ 0.55	$ 3.88	$ 2.77	$ 2.39
Diluted net income per common share attributable to D.R. Horton, Inc.	$ 1.22	$ 1.18	$ 0.91	$ 0.49	$ 0.82	$ 0.76	$ 0.60	$ 0.55	$ 3.81	$ 2.74	$ 2.36