Quarterly Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Summary of quarterly results of operations
Revenues	$ 3,741.3	$ 3,231.9	$ 2,767.9	$ 2,416.4	$ 3,172.5	$ 2,950.8	$ 2,398.0	$ 2,302.6	$ 12,157.4	$ 10,824.0	$ 8,024.9
Income before income taxes	433.0	378.6	300.5	241.3	338.8	333.8	230.1	220.7	1,353.5	1,123.4	814.2
Income Tax Expense (Benefit)	149.4	128.8	105.4	83.6	99.9	112.4	82.2	78.2	467.2	372.7	280.7
Net income	$ 283.6	$ 249.8	$ 195.1	$ 157.7	$ 238.9	$ 221.4	$ 147.9	$ 142.5	$ 886.3	$ 750.7	$ 533.5
Basic net income (loss) per common share	$ 0.76	$ 0.67	$ 0.53	$ 0.43	$ 0.65	$ 0.60	$ 0.40	$ 0.39	$ 2.39	$ 2.05	$ 1.57
Net income per common share assuming dilution	$ 0.75	$ 0.66	$ 0.52	$ 0.42	$ 0.64	$ 0.60	$ 0.40	$ 0.39	$ 2.36	$ 2.03	$ 1.50
Homebuilding [Member]
Summary of quarterly results of operations
Production Related Impairments or Charges	$ 15.4	$ 8.1	$ 6.0	$ 2.0	$ 26.3	$ 15.4	$ 12.5	$ 6.0	$ 31.4	$ 60.3	$ 85.2
Gross profit	$ 732.6	$ 625.8	$ 531.7	$ 468.9	$ 582.3	$ 556.0	$ 446.5	$ 438.6	2,359.2	2,023.3	1,589.9
Income before income taxes									$ 1,264.4	$ 1,018.3	$ 768.5