Quarterly Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Summary of quarterly results of operations
Revenues	$ 4,505.2	$ 4,435.3	$ 3,794.7	$ 3,332.7	$ 4,159.1	$ 3,776.4	$ 3,251.3	$ 2,904.2	$ 16,068.0	$ 14,091.0	$ 12,157.4
Income before income taxes	607.7	616.2	444.8	391.2	485.5	444.5	353.9	318.1	2,060.0	1,602.1	1,353.5
Income tax expense	138.8	162.5	94.0	202.4	172.3	155.5	124.7	111.2	597.7	563.7	467.2
Net income	468.9	453.7	350.8	188.8					1,462.3	1,038.4	886.3
Net income attributable to noncontrolling interests	2.8	(0.1)	(0.2)	(0.5)					2.0	0.0	0.0
Net income attributable to D.R. Horton, Inc.	$ 466.1	$ 453.8	$ 351.0	$ 189.3	$ 313.2	$ 289.0	$ 229.2	$ 206.9	$ 1,460.3	$ 1,038.4	$ 886.3
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
Homebuilding [Member]
Summary of quarterly results of operations
Revenues									$ 15,623.8	$ 13,741.5	$ 11,861.8
Income before income taxes									$ 1,957.2	$ 1,489.3	$ 1,264.4