Business Segment Information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Sales	$ 2,155.7	$ 1,980.1	$ 4,372.3	$ 3,862.6
Operating income (loss)	455.4	395.6	916.1	723.9
Contracts accounted for under percentage of completion [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	10.0	12.0
Industrial Gases - Global | Intersegment Eliminations
Segment Reporting Information [Line Items]
Sales	56.0	61.0	117.9	122.0
Jazan [Member] | Industrial Gases - Global
Segment Reporting Information [Line Items]
Sales	$ 60.0	$ 170.0	$ 150.0	$ 280.0