Basis of Presentation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Income tax expense (benefit)	$ 23.9	$ (2.1)	$ (231.9)	$ 43.9
Net Earnings (Loss)	$ 91.5	$ (2.1)	$ 386.4	$ 99.7
Earnings (Loss) per Share, Basic (in usd per share)	$ 1.33	$ (0.08)	$ 5.73	$ 1.35
Earnings (Loss) per Share, Diluted (in usd per share)	$ 1.20	$ (0.08)	$ 5.04	$ 1.25
Net Cash Provided by (Used in) Operating Activities			$ 263.6	$ (21.7)
Net Cash Provided by Financing Activities			$ 56.9	505.0
Accounting Standards Update 2016-09
Income tax expense (benefit)		$ (1.9)		(6.1)
Net Earnings (Loss)		$ 1.9		$ 6.1
Earnings (Loss) per Share, Basic (in usd per share)		$ 0.03		$ 0.09
Earnings (Loss) per Share, Diluted (in usd per share)		$ 0.03		$ 0.07
Net Cash Provided by (Used in) Operating Activities				$ 4.8
Net Cash Provided by Financing Activities				$ (4.8)