Supplemental Guarantor Information - Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016
ASSETS
Cash and cash equivalents	$ 1,010.8	$ 1,007.8	$ 993.2	$ 1,303.2
Restricted cash	55.4	16.5
Investments in subsidiaries	0.0	0.0
Inventories	10,144.4	9,237.1
Investment in unconsolidated entities	32.1	0.0
Mortgage loans held for sale	658.2	587.3
Deferred income taxes	219.9	365.0
Property and equipment, net	380.4	325.0
Other assets	607.7	565.9
Goodwill	109.2	80.0
Intercompany receivables	0.0	0.0
Total assets	13,218.1	12,184.6
LIABILITIES & EQUITY
Accounts payable and other liabilities	1,612.3	1,565.4
Intercompany payables	0.0	0.0
Notes payable	3,233.9	2,871.6
Total liabilities	4,846.2	4,437.0
Stockholders’ equity	8,198.9	7,747.1
Noncontrolling interests	173.0	0.5
Total equity	8,371.9	7,747.6
Total liabilities and equity	13,218.1	12,184.6
Eliminations [Member]
ASSETS
Cash and cash equivalents	0.0	0.0	0.0	0.0
Restricted cash	0.0	0.0
Investments in subsidiaries	(5,753.5)	(4,812.6)
Inventories	(1.8)	0.0
Investment in unconsolidated entities	0.0
Mortgage loans held for sale	0.0	0.0
Deferred income taxes	0.0	0.0
Property and equipment, net	(6.6)	(5.8)
Other assets	(21.4)	0.0
Goodwill	0.0	0.0
Intercompany receivables	(778.4)	(1,047.7)
Total assets	(6,561.7)	(5,866.1)
LIABILITIES & EQUITY
Accounts payable and other liabilities	(23.5)	(2.0)
Intercompany payables	(778.4)	(1,047.7)
Notes payable	0.0	0.0
Total liabilities	(801.9)	(1,049.7)
Stockholders’ equity	(5,759.8)	(4,816.4)
Noncontrolling interests	0.0	0.0
Total equity	(5,759.8)	(4,816.4)
Total liabilities and equity	(6,561.7)	(5,866.1)
D.R. Horton, Inc. [Member]
ASSETS
Cash and cash equivalents	372.1	780.9	812.5	1,076.4
Restricted cash	6.7	7.8
Investments in subsidiaries	5,753.5	4,812.6
Inventories	3,975.9	3,540.4
Investment in unconsolidated entities	0.0
Mortgage loans held for sale	0.0	0.0
Deferred income taxes	84.8	138.5
Property and equipment, net	110.8	104.8
Other assets	255.0	245.5
Goodwill	0.0	0.0
Intercompany receivables	778.4	1,047.7
Total assets	11,337.2	10,678.2
LIABILITIES & EQUITY
Accounts payable and other liabilities	515.0	483.9
Intercompany payables	0.0	0.0
Notes payable	2,616.9	2,443.4
Total liabilities	3,131.9	2,927.3
Stockholders’ equity	8,205.3	7,750.9
Noncontrolling interests	0.0	0.0
Total equity	8,205.3	7,750.9
Total liabilities and equity	11,337.2	10,678.2
Guarantor Subsidiaries [Member]
ASSETS
Cash and cash equivalents	114.9	154.5	95.2	154.0
Restricted cash	2.7	1.5
Investments in subsidiaries	0.0	0.0
Inventories	5,850.1	5,579.9
Investment in unconsolidated entities	0.0
Mortgage loans held for sale	0.0	0.0
Deferred income taxes	131.1	223.6
Property and equipment, net	63.7	59.7
Other assets	286.4	259.7
Goodwill	80.0	80.0
Intercompany receivables	0.0	0.0
Total assets	6,528.9	6,358.9
LIABILITIES & EQUITY
Accounts payable and other liabilities	949.2	956.9
Intercompany payables	545.2	732.2
Notes payable	6.3	8.2
Total liabilities	1,500.7	1,697.3
Stockholders’ equity	5,028.2	4,661.6
Noncontrolling interests	0.0	0.0
Total equity	5,028.2	4,661.6
Total liabilities and equity	6,528.9	6,358.9
Non-Guarantor Subsidiaries [Member]
ASSETS
Cash and cash equivalents	523.8	72.4	$ 85.5	$ 72.8
Restricted cash	46.0	7.2
Investments in subsidiaries	0.0	0.0
Inventories	320.2	116.8
Investment in unconsolidated entities	32.1
Mortgage loans held for sale	658.2	587.3
Deferred income taxes	4.0	2.9
Property and equipment, net	212.5	166.3
Other assets	87.7	60.7
Goodwill	29.2	0.0
Intercompany receivables	0.0	0.0
Total assets	1,913.7	1,013.6
LIABILITIES & EQUITY
Accounts payable and other liabilities	171.6	126.6
Intercompany payables	233.2	315.5
Notes payable	610.7	420.0
Total liabilities	1,015.5	862.1
Stockholders’ equity	725.2	151.0
Noncontrolling interests	173.0	0.5
Total equity	898.2	151.5
Total liabilities and equity	$ 1,913.7	$ 1,013.6