Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share Reconciliation [Abstract]
Net Income (Loss) Attributable to Parent	$ 829.0	$ 630.7	$ 482.7	$ 431.3	$ 505.3	$ 474.8	$ 351.3	$ 287.2	$ 2,373.7	$ 1,618.5	$ 1,460.3
Denominator:
Denominator for basic earnings per share - weighted average common shares									365.5	372.6	376.6
Effect of dilutive securities:
Employee stock awards									4.7	4.8	6.8
Denominator for diluted earnings per share - adjusted weighted average common shares									370.2	377.4	383.4
Basic net income per common share attributable to D.R. Horton, Inc.	$ 2.28	$ 1.73	$ 1.32	$ 1.17	$ 1.37	$ 1.28	$ 0.94	$ 0.77	$ 6.49	$ 4.34	$ 3.88
Diluted net income per common share attributable to D.R. Horton, Inc.	$ 2.24	$ 1.72	$ 1.30	$ 1.16	$ 1.35	$ 1.26	$ 0.93	$ 0.76	$ 6.41	$ 4.29	$ 3.81