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Supplemental Information (Narrative) (Details) $ in Millions, ¥ in Billions	3 Months Ended			6 Months Ended
	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2019 CNY (¥)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 CNY (¥)	Apr. 26, 2018 CNY (¥)
Debt Instrument [Line Items]
Facility closure	$ 0.0	$ 29.0	$ 0.0	$ 29.0	$ 0.0
Sales to related parties	80.0		$ 70.0	165.0	$ 175.0
Long-term debt – related party	369.2			369.2			$ 384.3
Current portion of long-term debt – related party	24.1			24.1
Liability for expected cash payments to or on behalf of related party	$ 82.7			$ 82.7		¥ 0.6	$ 330.0	¥ 2.2	¥ 2.3
Joint Venture \| Air Products Lu'an Changzhi Co Ltd
Debt Instrument [Line Items]
Ownership interest by Air Products (percent)									60.00%
Loans Payable \| Lu'An Loan To Joint Venture
Debt Instrument [Line Items]
Long-term debt – related party \| ¥									¥ 2.6