Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 10,321.2	$ 7,261.1	$ 10,185.5	$ 7,213.4
Other comprehensive income before reclassifications	143.4		270.3
Amounts reclassified from AOCL	19.1		45.9
Total Other Comprehensive Income	162.5	223.0	316.2	(15.0)
Amount attributable to noncontrolling interests	2.2	5.0	4.1	1.9
Ending balance	10,693.2	$ 9,420.2	10,693.2	$ 9,420.2
Derivatives qualifying as hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(61.8)		(53.1)
Other comprehensive income before reclassifications	17.8		8.3
Amounts reclassified from AOCL	(7.5)		(6.7)
Total Other Comprehensive Income	10.3		1.6
Amount attributable to noncontrolling interests	(0.1)		(0.1)
Ending balance	(51.4)		(51.4)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(649.5)		(787.1)
Other comprehensive income before reclassifications	125.6		262.0
Amounts reclassified from AOCL	0.0		3.1
Total Other Comprehensive Income	125.6		265.1
Amount attributable to noncontrolling interests	2.3		4.2
Ending balance	(526.2)		(526.2)
Pension and postretirement benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(984.3)		(1,007.2)
Other comprehensive income before reclassifications	0.0		0.0
Amounts reclassified from AOCL	26.6		49.5
Total Other Comprehensive Income	26.6		49.5
Amount attributable to noncontrolling interests	0.0		0.0
Ending balance	(957.7)		(957.7)
AOCL attributable to Air Products
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,695.6)		(1,847.4)
Ending balance	$ (1,535.3)		$ (1,535.3)