Quarterly Results of Operations (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2011
Summary of quarterly results of operations
Revenues	$ 1,859.8	$ 1,692.8	$ 1,431.6	$ 1,275.1	$ 1,336.2	$ 1,150.0	$ 961.2	$ 906.6	$ 6,259.3		$ 4,354.0		$ 3,636.8
Income before income taxes	202.8	205.1	142.1	107.9	99.2	72.2	42.3	29.2	657.8	[1]	242.9	[1]	12.1	[1]
Income Tax Expense (Benefit)	63.3	59.1	31.1	41.6	(0.9)	(715.6)	1.7	1.5	195.1		(713.4)		(59.7)
Net income	139.5	146.0	111.0	66.3	100.1	787.8	40.6	27.7	462.7		956.3		71.8
Basic net income (loss) per common share	$ 0.43	$ 0.45	$ 0.35	$ 0.21	$ 0.31	$ 2.47	$ 0.13	$ 0.09	$ 1.44		$ 3.01		$ 0.23
Diluted net income (loss) per common share	$ 0.40	$ 0.42	$ 0.32	$ 0.20	$ 0.30	$ 2.22	$ 0.13	$ 0.09	$ 1.33		$ 2.77		$ 0.23
Homebuilding [Member]
Summary of quarterly results of operations
Gross profit	371.4	349.1	281.2	230.9	232.5	198.3	164.4	148.6	1,232.4		743.8		526.3
Income before income taxes									$ 592.3	[1]	$ 203.7	[1]	$ (7.0)	[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 interest expense and those expenses associated with the corporate office are allocated to each segment based on the segment’s inventory balances.