Supplemental Guarantor Information - Statement of Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
OPERATING ACTIVITIES
Net cash (used in) provided by operating activities	$ (98.8)	$ (135.7)
INVESTING ACTIVITIES
Expenditures for property and equipment	(79.0)	(57.5)
Proceeds from sale of assets	253.4	0.0
Decrease (increase) in restricted cash	(38.9)	(8.9)
Investment in unconsolidated entities	(0.1)	0.0
Return of investment in unconsolidated entities	15.2	0.0
Net principal decrease of other mortgage loans and real estate owned	0.0	1.0
Purchases of debt securities collateralized by residential real estate	0.0	(3.9)
Intercompany advances	0.0	0.0
Payments related to business acquisitions, net of cash acquired	(158.1)	(4.1)
Net cash (used in) provided by investing activities	(7.5)	(73.4)
FINANCING ACTIVITIES
Proceeds from notes payable	1,913.6	0.0
Repayment of notes payable	(1,752.5)	(0.5)
Advances (payments) on mortgage repurchase facility, net	69.8	(54.0)
Intercompany advances	0.0	0.0
Proceeds from stock associated with certain employee benefit plans	32.7	24.7
Excess income tax benefit from employee stock awards	0.0	8.7
Cash paid for shares withheld for taxes	(10.3)	(5.1)
Cash dividends paid	(94.1)	(74.7)
Repurchases of common stock	(47.9)	0.0
Distributions to noncontrolling interests, net	(2.0)	0.0
Net cash (used in) provided by financing activities	109.3	(100.9)
(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	3.0	(310.0)
Cash and cash equivalents at beginning of period	1,007.8	1,303.2
Cash and cash equivalents at end of period	1,010.8	993.2
Eliminations [Member]
OPERATING ACTIVITIES
Net cash (used in) provided by operating activities	(37.0)	(50.0)
INVESTING ACTIVITIES
Expenditures for property and equipment	5.0	0.0
Proceeds from sale of assets	0.0
Decrease (increase) in restricted cash	0.0	0.0
Investment in unconsolidated entities	0.0
Return of investment in unconsolidated entities	0.0
Net principal decrease of other mortgage loans and real estate owned		0.0
Purchases of debt securities collateralized by residential real estate		0.0
Intercompany advances	(266.3)	(123.8)
Payments related to business acquisitions, net of cash acquired	0.0	0.0
Net cash (used in) provided by investing activities	(261.3)	(123.8)
FINANCING ACTIVITIES
Proceeds from notes payable	0.0
Repayment of notes payable	0.0	0.0
Advances (payments) on mortgage repurchase facility, net	0.0	0.0
Intercompany advances	266.3	123.8
Proceeds from stock associated with certain employee benefit plans	0.0	0.0
Excess income tax benefit from employee stock awards		0.0
Cash paid for shares withheld for taxes	0.0	0.0
Cash dividends paid	32.0	50.0
Repurchases of common stock	0.0
Distributions to noncontrolling interests, net	0.0
Net cash (used in) provided by financing activities	298.3	173.8
(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	0.0	0.0
Cash and cash equivalents at beginning of period	0.0	0.0
Cash and cash equivalents at end of period	0.0	0.0
D.R. Horton, Inc. [Member]
OPERATING ACTIVITIES
Net cash (used in) provided by operating activities	(147.3)	(303.6)
INVESTING ACTIVITIES
Expenditures for property and equipment	(21.4)	(28.4)
Proceeds from sale of assets	0.0
Decrease (increase) in restricted cash	1.1	(1.3)
Investment in unconsolidated entities	0.0
Return of investment in unconsolidated entities	0.0
Net principal decrease of other mortgage loans and real estate owned		0.0
Purchases of debt securities collateralized by residential real estate		(3.9)
Intercompany advances	266.3	123.8
Payments related to business acquisitions, net of cash acquired	(560.0)	(4.1)
Net cash (used in) provided by investing activities	(314.0)	86.1
FINANCING ACTIVITIES
Proceeds from notes payable	1,912.3
Repayment of notes payable	(1,740.2)	0.0
Advances (payments) on mortgage repurchase facility, net	0.0	0.0
Intercompany advances	0.0	0.0
Proceeds from stock associated with certain employee benefit plans	32.7	24.7
Excess income tax benefit from employee stock awards		8.7
Cash paid for shares withheld for taxes	(10.3)	(5.1)
Cash dividends paid	(94.1)	(74.7)
Repurchases of common stock	(47.9)
Distributions to noncontrolling interests, net	0.0
Net cash (used in) provided by financing activities	52.5	(46.4)
(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(408.8)	(263.9)
Cash and cash equivalents at beginning of period	780.9	1,076.4
Cash and cash equivalents at end of period	372.1	812.5
Guarantor Subsidiaries [Member]
OPERATING ACTIVITIES
Net cash (used in) provided by operating activities	269.9	130.3
INVESTING ACTIVITIES
Expenditures for property and equipment	(15.0)	(11.7)
Proceeds from sale of assets	0.0
Decrease (increase) in restricted cash	(1.2)	(0.3)
Investment in unconsolidated entities	0.0
Return of investment in unconsolidated entities	0.0
Net principal decrease of other mortgage loans and real estate owned		0.0
Purchases of debt securities collateralized by residential real estate		0.0
Intercompany advances	0.0	0.0
Payments related to business acquisitions, net of cash acquired	0.0	0.0
Net cash (used in) provided by investing activities	(16.2)	(12.0)
FINANCING ACTIVITIES
Proceeds from notes payable	0.0
Repayment of notes payable	(2.3)	(0.5)
Advances (payments) on mortgage repurchase facility, net	0.0	0.0
Intercompany advances	(291.0)	(176.6)
Proceeds from stock associated with certain employee benefit plans	0.0	0.0
Excess income tax benefit from employee stock awards		0.0
Cash paid for shares withheld for taxes	0.0	0.0
Cash dividends paid	0.0	0.0
Repurchases of common stock	0.0
Distributions to noncontrolling interests, net	0.0
Net cash (used in) provided by financing activities	(293.3)	(177.1)
(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(39.6)	(58.8)
Cash and cash equivalents at beginning of period	154.5	154.0
Cash and cash equivalents at end of period	114.9	95.2
Non-Guarantor Subsidiaries [Member]
OPERATING ACTIVITIES
Net cash (used in) provided by operating activities	(184.4)	87.6
INVESTING ACTIVITIES
Expenditures for property and equipment	(47.6)	(17.4)
Proceeds from sale of assets	253.4
Decrease (increase) in restricted cash	(38.8)	(7.3)
Investment in unconsolidated entities	(0.1)
Return of investment in unconsolidated entities	15.2
Net principal decrease of other mortgage loans and real estate owned		1.0
Purchases of debt securities collateralized by residential real estate		0.0
Intercompany advances	0.0	0.0
Payments related to business acquisitions, net of cash acquired	401.9	0.0
Net cash (used in) provided by investing activities	584.0	(23.7)
FINANCING ACTIVITIES
Proceeds from notes payable	1.3
Repayment of notes payable	(10.0)	0.0
Advances (payments) on mortgage repurchase facility, net	69.8	(54.0)
Intercompany advances	24.7	52.8
Proceeds from stock associated with certain employee benefit plans	0.0	0.0
Excess income tax benefit from employee stock awards		0.0
Cash paid for shares withheld for taxes	0.0	0.0
Cash dividends paid	(32.0)	(50.0)
Repurchases of common stock	0.0
Distributions to noncontrolling interests, net	(2.0)
Net cash (used in) provided by financing activities	51.8	(51.2)
(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	451.4	12.7
Cash and cash equivalents at beginning of period	72.4	72.8
Cash and cash equivalents at end of period	$ 523.8	$ 85.5