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Supplemental Information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Disclosure Text Block Supplement [Abstract]
Net proceeds from sale of property	$ 44.1
Company headquarters relocation income (expense)	33.8	$ 0.0		$ 33.8	$ 0.0
Facility closure	0.0	0.0	$ 29.0	0.0	29.0
Related Party Transaction [Line Items]
Trade receivables, net	205.0			205.0		$ 130.0
Equity affiliate and joint venture partner
Related Party Transaction [Line Items]
Sales to and other income from related parties	$ 90.0	$ 80.0		$ 180.0	$ 165.0