Quarterly Results of Operations (Unaudited) (Details) (USD $) In Millions, except Per Share data	3 Months Ended								12 Months Ended
	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2009
Summary of quarterly results of operations
Revenues	$ 1,098.3	$ 999.2	$ 751.1	$ 788.2	$ 948.4	$ 1,406.1	$ 913.5	$ 1,132.2	$ 3,636.8	$ 4,400.2	$ 3,657.6
Gross profit	160.0	151.3	104.8	110.2	127.8	206.8	159.2	188.3
Income (loss) before income taxes	33.8	28.9	(30.8)	(19.9)	(1.7)	46.3	12.1	42.8	12.1	99.5	(556.8)
Income tax expense (benefit)	(1.9)	0.2	(58.6)	0.5	7.2	(4.2)	0.7	(149.2)	(59.7)	(145.6)	(7.0)
Net income (loss)	$ 35.7	$ 28.7	$ 27.8	$ (20.4)	$ (8.9)	$ 50.5	$ 11.4	$ 192.0	$ 71.8	$ 245.1	$ (549.8)
Basic net income (loss) per common share	$ 0.11	$ 0.09	$ 0.09	$ (0.06)	$ (0.03)	$ 0.16	$ 0.04	$ 0.60	$ 0.23	$ 0.77	$ (1.73)
Diluted net income (loss) per common share	$ 0.11	$ 0.09	$ 0.09	$ (0.06)	$ (0.03)	$ 0.16	$ 0.04	$ 0.56	$ 0.23	$ 0.77	$ (1.73)