Business Segment Information (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Sales	$ 2,259.0	$ 2,121.9	$ 6,631.3	$ 5,984.5
Operating income (loss)	515.8	258.7	1,431.9	982.6
Contracts accounted for under percentage of completion
Segment Reporting Information [Line Items]
Operating income (loss)	15.0	15.0	25.0	27.0
Industrial Gases - Global | Intersegment Eliminations
Segment Reporting Information [Line Items]
Sales	68.7	57.4	186.6	179.4
Jazan | Industrial Gases - Global
Segment Reporting Information [Line Items]
Sales	$ 50.0	$ 140.0	$ 200.0	$ 420.0