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Supplemental Information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Disclosure Text Block Supplement [Abstract]
Facility closure	$ 23.2	$ 0.0	$ 23.2	$ 0.0
Net proceeds from sale of property		44.1
Company headquarters relocation income (expense)	0.0	33.8	0.0	33.8
Related Party Transaction [Line Items]
Trade receivables, net	110.0		110.0		$ 95.0
Related party debt, including current portion	352.5		352.5		$ 338.5
Change in Accounting Estimate [Line Items]
Operating income (loss)	(548.5)	(577.2)	(1,087.6)	(1,138.2)
Equity affiliate and joint venture partner
Related Party Transaction [Line Items]
Sales to and other income from related parties	$ 40.0	$ 90.0	90.0	$ 180.0
Contracts accounted for under percentage of completion \| Industrial Gases - Global
Change in Accounting Estimate [Line Items]
Operating income (loss)			$ 7.0