Quarterly Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Summary of quarterly results of operations
Revenues	$ 6,400.4	$ 5,390.0	$ 4,500.0	$ 4,020.7	$ 5,038.9	$ 4,906.3	$ 4,128.7	$ 3,519.0	$ 20,311.1	$ 17,592.9	$ 16,068.0
Income before income taxes	1,056.1	782.4	621.3	523.3	660.1	626.7	462.8	375.7	2,983.0	2,125.3	2,060.0
Income tax expense	224.9	149.5	137.3	90.8	156.2	153.1	108.4	89.0	602.5	506.7	597.7
Net income	831.2	632.9	484.0	432.5	503.9	473.6	354.4	286.7	2,380.5	1,618.6	1,462.3
Net income attributable to noncontrolling interests	2.2	2.2	1.3	1.2	(1.4)	(1.2)	3.1	(0.5)	6.8	0.1	2.0
Net income attributable to D.R. Horton, Inc.	$ 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
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