Business Segment and Geographic Information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Sales	$ 2,298.9	$ 2,259.0	$ 2,155.7	$ 2,216.6	$ 2,203.1	$ 2,121.9	$ 1,980.1	$ 1,882.5	$ 8,930.2	$ 8,187.6	$ 7,503.7
Export sales to third-party customers									33.1	64.2	134.9
Industrial Gases - Global | Intersegment Eliminations
Segment Reporting Information [Line Items]
Sales									$ 254.3	$ 239.0	$ 232.4