Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 10,693.2	$ 9,420.2	$ 10,185.5	$ 7,213.4
Other comprehensive income (loss) before reclassifications	(365.3)		(95.0)
Amounts reclassified from AOCL	8.3		54.2
Total Other Comprehensive Income (Loss)	(357.0)	176.8	(40.8)	161.8
Amount attributable to noncontrolling interests	(14.5)	0.2	(10.4)	2.1
Ending balance	10,810.0	$ 9,509.9	10,810.0	$ 9,509.9
Derivatives qualifying as hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(51.4)		(53.1)
Other comprehensive income (loss) before reclassifications	27.1		35.4
Amounts reclassified from AOCL	(17.7)		(24.4)
Total Other Comprehensive Income (Loss)	9.4		11.0
Amount attributable to noncontrolling interests	0.1		0.0
Ending balance	(42.1)		(42.1)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(526.2)		(787.1)
Other comprehensive income (loss) before reclassifications	(392.4)		(130.4)
Amounts reclassified from AOCL	0.0		3.1
Total Other Comprehensive Income (Loss)	(392.4)		(127.3)
Amount attributable to noncontrolling interests	(14.6)		(10.4)
Ending balance	(904.0)		(904.0)
Pension and postretirement benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(957.7)		(1,007.2)
Other comprehensive income (loss) before reclassifications	0.0		0.0
Amounts reclassified from AOCL	26.0		75.5
Total Other Comprehensive Income (Loss)	26.0		75.5
Amount attributable to noncontrolling interests	0.0		0.0
Ending balance	(931.7)		(931.7)
AOCL attributable to Air Products
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,535.3)		(1,847.4)
Ending balance	$ (1,877.8)		$ (1,877.8)