Quarterly Results of Operations (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	0 Months Ended	3 Months Ended								12 Months Ended
	Apr. 02, 2012	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
Quarterly Financial Data [Line Items]
Valuation Allowance, Deferred Tax Asset, Change in Amount	$ 753.2					$ (2.9)		$ 18.7
Summary of quarterly results of operations
Revenues		2,472.3	2,147.0	1,735.0	1,670.6	1,859.8	1,692.8	1,431.6	1,275.1	8,024.9		6,259.3		4,354.0
Income before income taxes		250.8	171.8	201.9	189.7	202.8	205.1	142.1	107.9	814.2	[1]	657.8	[1]	242.9	[1]
Income Tax Expense (Benefit)		84.5	58.7	70.9	66.5	63.3	59.1	31.1	41.6	280.7		195.1		(713.4)
Net income		166.3	113.1	131.0	123.2	139.5	146.0	111.0	66.3	533.5		462.7		956.3
Basic net income (loss) per common share		$ 0.46	$ 0.32	$ 0.40	$ 0.38	$ 0.43	$ 0.45	$ 0.35	$ 0.21	$ 1.57		$ 1.44		$ 3.01
Diluted net income (loss) per common share		$ 0.45	$ 0.32	$ 0.38	$ 0.36	$ 0.40	$ 0.42	$ 0.32	$ 0.20	$ 1.50		$ 1.33		$ 2.77
Homebuilding [Member]
Summary of quarterly results of operations
Production Related Impairments or Charges		21.3	56.8	4.4	2.6	27.1	0.8	1.8	1.3	85.2		31.1		6.2
Gross profit		473.7	377.4	376.8	362.0	371.4	349.1	281.2	230.9	1,589.9		1,232.4		743.8
Income before income taxes										$ 768.8	[1]	$ 592.3	[1]	$ 203.7	[1]

[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 revenue, while those expenses associated with the corporate office are allocated to each segment based on the segment’s inventory balances.