Quarterly Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Summary of quarterly results of operations
Revenues	$ 5,038.9	$ 4,906.3	$ 4,128.7	$ 3,519.0	$ 4,505.2	$ 4,435.3	$ 3,794.7	$ 3,332.7	$ 17,592.9	$ 16,068.0	$ 14,091.0
Income before income taxes	660.1	626.7	462.8	375.7	607.7	616.2	444.8	391.2	2,125.3	2,060.0	1,602.1
Income tax expense	156.2	153.1	108.4	89.0	138.8	162.5	94.0	202.4	506.7	597.7	563.7
Net income	503.9	473.6	354.4	286.7	468.9	453.7	350.8	188.8	1,618.6	1,462.3	1,038.4
Net income attributable to noncontrolling interests	(1.4)	(1.2)	3.1	(0.5)	2.8	(0.1)	(0.2)	(0.5)	0.1	2.0	0.0
Net income attributable to D.R. Horton, Inc.	$ 505.3	$ 474.8	$ 351.3	$ 287.2	$ 466.1	$ 453.8	$ 351.0	$ 189.3	$ 1,618.5	$ 1,460.3	$ 1,038.4
Basic net income per common share attributable to D.R. Horton, Inc.	$ 1.37	$ 1.28	$ 0.94	$ 0.77	$ 1.24	$ 1.20	$ 0.93	$ 0.50	$ 4.34	$ 3.88	$ 2.77
Diluted net income per common share attributable to D.R. Horton, Inc.	$ 1.35	$ 1.26	$ 0.93	$ 0.76	$ 1.22	$ 1.18	$ 0.91	$ 0.49	$ 4.29	$ 3.81	$ 2.74