Quarterly Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended								12 Months Ended
		Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2015		Sep. 30, 2014		Sep. 30, 2013
Quarterly Financial Data [Line Items]
Valuation Allowance, Deferred Tax Asset, Change in Amount		$ 17.5
Summary of quarterly results of operations
Revenues		3,172.5	$ 2,950.8	$ 2,398.0	$ 2,302.6	$ 2,472.3	$ 2,147.0	$ 1,735.0	$ 1,670.6	$ 10,824.0		$ 8,024.9		$ 6,259.3
Income before income taxes		338.8	333.8	230.1	220.7	250.8	171.8	201.9	189.7	1,123.4	[1]	814.2	[1]	657.8	[1]
Income Tax Expense (Benefit)		99.9	112.4	82.2	78.2	84.5	58.7	70.9	66.5	372.7		280.7		195.1
Net income		$ 238.9	$ 221.4	$ 147.9	$ 142.5	$ 166.3	$ 113.1	$ 131.0	$ 123.2	$ 750.7		$ 533.5		$ 462.7
Basic net income (loss) per common share		$ 0.65	$ 0.60	$ 0.40	$ 0.39	$ 0.46	$ 0.32	$ 0.40	$ 0.38	$ 2.05		$ 1.57		$ 1.44
Net income per common share assuming dilution		$ 0.64	$ 0.60	$ 0.40	$ 0.39	$ 0.45	$ 0.32	$ 0.38	$ 0.36	$ 2.03		$ 1.50		$ 1.33
Homebuilding [Member]
Summary of quarterly results of operations
Production Related Impairments or Charges		$ 26.3	$ 15.4	$ 12.5	$ 6.0	$ 21.3	$ 56.8	$ 4.4	$ 2.6	$ 60.3		$ 85.2		$ 31.1
Gross profit		$ 582.3	$ 556.0	$ 446.5	$ 438.6	$ 473.7	$ 377.4	$ 376.8	$ 362.0	2,023.3		1,589.9		1,232.4
Income before income taxes	[1]									$ 1,018.3		$ 768.8		$ 592.3

[1] Expenses maintained at the corporate level consist primarily of interest and property taxes, which are capitalized and amortized to cost of sales or expensed directly, and the expenses related to operating the Company’s corporate office. The amortization of capitalized interest and property taxes is allocated to each segment based on the segment’s cost of sales, while those expenses associated with the corporate office are allocated to each segment based on the segment’s inventory balances.