Supplemental Guarantor Information - Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018
OPERATING ACTIVITIES
Net cash (used in) provided by operating activities				$ (461.7)	$ (98.8)
INVESTING ACTIVITIES
Expenditures for property and equipment				(69.8)	(39.5)
Proceeds from sale of assets				83.8	253.4
Expenditures related to multi-family rental properties				(28.3)	(39.5)
Return of investment in unconsolidated entities				4.4	15.1
Net principal increase of other mortgage loans and real estate owned				(1.6)	0.0
Intercompany advances				0.0	0.0
Payments related to business acquisitions				309.6	158.1
Net cash (used in) provided by investing activities				(321.1)	31.4
FINANCING ACTIVITIES
Proceeds from notes payable				1,815.0	1,913.6
Repayment of notes payable				(1,531.0)	(1,752.5)
Advances (payments) on mortgage repurchase facility, net				53.0	69.8
Intercompany advances				0.0	0.0
Proceeds from stock associated with certain employee benefit plans				22.3	32.7
Cash paid for shares withheld for taxes	$ (15.4)	$ (4.1)	$ (10.3)	(19.5)	(10.3)
Cash dividends paid				(111.9)	(94.1)
Repurchases of common stock				(216.2)	(47.9)
Distributions to noncontrolling interests, net				(3.7)	(2.0)
Net cash (used in) provided by financing activities				8.0	109.3
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect				(774.8)	41.9
Cash, cash equivalents and restricted cash at beginning of period		1,506.0	1,024.3	1,506.0	1,024.3
Cash, cash equivalents and restricted cash at end of period	731.2			731.2	1,066.2
Eliminations [Member]
OPERATING ACTIVITIES
Net cash (used in) provided by operating activities				(78.7)	(37.0)
INVESTING ACTIVITIES
Expenditures for property and equipment				0.0	0.0
Proceeds from sale of assets				0.0	0.0
Expenditures related to multi-family rental properties				0.0	5.0
Return of investment in unconsolidated entities				0.0	0.0
Net principal increase of other mortgage loans and real estate owned				0.0
Intercompany advances				42.4	(266.3)
Payments related to business acquisitions				0.0	0.0
Net cash (used in) provided by investing activities				42.4	(261.3)
FINANCING ACTIVITIES
Proceeds from notes payable				0.0	0.0
Repayment of notes payable				0.0	0.0
Advances (payments) on mortgage repurchase facility, net				0.0	0.0
Intercompany advances				(42.4)	266.3
Proceeds from stock associated with certain employee benefit plans				0.0	0.0
Cash paid for shares withheld for taxes				0.0	0.0
Cash dividends paid				78.7	32.0
Repurchases of common stock				0.0	0.0
Distributions to noncontrolling interests, net				0.0	0.0
Net cash (used in) provided by financing activities				36.3	298.3
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect				0.0	0.0
Cash, cash equivalents and restricted cash at beginning of period		0.0	0.0	0.0	0.0
Cash, cash equivalents and restricted cash at end of period	0.0			0.0	0.0
D.R. Horton, Inc. [Member]
OPERATING ACTIVITIES
Net cash (used in) provided by operating activities				(76.5)	(147.3)
INVESTING ACTIVITIES
Expenditures for property and equipment				(16.7)	(21.4)
Proceeds from sale of assets				10.4	0.0
Expenditures related to multi-family rental properties				0.0	0.0
Return of investment in unconsolidated entities				0.0	0.0
Net principal increase of other mortgage loans and real estate owned				0.0
Intercompany advances				(42.4)	266.3
Payments related to business acquisitions				301.3	560.0
Net cash (used in) provided by investing activities				(350.0)	(315.1)
FINANCING ACTIVITIES
Proceeds from notes payable				1,775.0	1,912.3
Repayment of notes payable				(1,524.9)	(1,740.2)
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				22.3	32.7
Cash paid for shares withheld for taxes				(19.5)	(10.3)
Cash dividends paid				(111.9)	(94.1)
Repurchases of common stock				(216.2)	(47.9)
Distributions to noncontrolling interests, net				0.0	0.0
Net cash (used in) provided by financing activities				(75.2)	52.5
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect				(501.7)	(409.9)
Cash, cash equivalents and restricted cash at beginning of period		914.7	788.7	914.7	788.7
Cash, cash equivalents and restricted cash at end of period	413.0			413.0	378.8
Guarantor Subsidiaries [Member]
OPERATING ACTIVITIES
Net cash (used in) provided by operating activities				(61.5)	269.9
INVESTING ACTIVITIES
Expenditures for property and equipment				(16.9)	(15.0)
Proceeds from sale of assets				0.0	0.0
Expenditures related to multi-family rental properties				0.0	0.0
Return of investment in unconsolidated entities				0.0	0.0
Net principal increase of other mortgage loans and real estate owned				0.0
Intercompany advances				0.0	0.0
Payments related to business acquisitions				0.0	0.0
Net cash (used in) provided by investing activities				(16.9)	(15.0)
FINANCING ACTIVITIES
Proceeds from notes payable				0.0	0.0
Repayment of notes payable				(1.1)	(2.3)
Advances (payments) on mortgage repurchase facility, net				0.0	0.0
Intercompany advances				24.9	(291.0)
Proceeds from stock associated with certain employee benefit plans				0.0	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	0.0
Distributions to noncontrolling interests, net				0.0	0.0
Net cash (used in) provided by financing activities				23.8	(293.3)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect				(54.6)	(38.4)
Cash, cash equivalents and restricted cash at beginning of period		160.7	156.0	160.7	156.0
Cash, cash equivalents and restricted cash at end of period	106.1			106.1	117.6
Non-Guarantor Subsidiaries [Member]
OPERATING ACTIVITIES
Net cash (used in) provided by operating activities				(245.0)	(184.4)
INVESTING ACTIVITIES
Expenditures for property and equipment				(36.2)	(3.1)
Proceeds from sale of assets				73.4	253.4
Expenditures related to multi-family rental properties				(28.3)	(44.5)
Return of investment in unconsolidated entities				4.4	15.1
Net principal increase of other mortgage loans and real estate owned				(1.6)
Intercompany advances				0.0	0.0
Payments related to business acquisitions				8.3	401.9
Net cash (used in) provided by investing activities				3.4	622.8
FINANCING ACTIVITIES
Proceeds from notes payable				40.0	1.3
Repayment of notes payable				(5.0)	(10.0)
Advances (payments) on mortgage repurchase facility, net				53.0	69.8
Intercompany advances				17.5	24.7
Proceeds from stock associated with certain employee benefit plans				0.0	0.0
Cash paid for shares withheld for taxes				0.0	0.0
Cash dividends paid				(78.7)	(32.0)
Repurchases of common stock				0.0	0.0
Distributions to noncontrolling interests, net				(3.7)	(2.0)
Net cash (used in) provided by financing activities				23.1	51.8
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect				(218.5)	490.2
Cash, cash equivalents and restricted cash at beginning of period		$ 430.6	$ 79.6	430.6	79.6
Cash, cash equivalents and restricted cash at end of period	$ 212.1			$ 212.1	$ 569.8