Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 11,203.4	$ 10,321.2	$ 11,176.3	$ 10,185.5
Other comprehensive income (loss) before reclassifications	15.9		(66.4)
Amounts reclassified from AOCL	55.6		67.7
Total Other Comprehensive Income	71.5	162.5	1.3	316.2
Amount attributable to noncontrolling interests	5.1	2.2	4.2	4.1
Ending balance	11,503.4	10,693.2	11,503.4	10,693.2
Derivatives qualifying as hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(50.9)		(37.6)
Other comprehensive income (loss) before reclassifications	(35.4)		(45.7)
Amounts reclassified from AOCL	36.9		33.8
Total Other Comprehensive Income	1.5		(11.9)
Amount attributable to noncontrolling interests	0.1		0.0
Ending balance	(49.5)		(49.5)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,077.1)		(1,009.8)
Other comprehensive income (loss) before reclassifications	51.3		(16.8)
Amounts reclassified from AOCL	0.0		0.0
Total Other Comprehensive Income	51.3		(16.8)
Amount attributable to noncontrolling interests	5.0		4.2
Ending balance	(1,030.8)		(1,030.8)
Pension and postretirement benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(683.2)		(694.5)
Other comprehensive income (loss) before reclassifications	0.0		(3.9)
Amounts reclassified from AOCL	18.7		33.9
Total Other Comprehensive Income	18.7		30.0
Amount attributable to noncontrolling interests	0.0		0.0
Ending balance	(664.5)		(664.5)
AOCL attributable to Air Products
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,811.2)	(1,695.6)	(1,741.9)	(1,847.4)
Total Other Comprehensive Income	66.4	160.3	(2.9)	312.1
Ending balance	$ (1,744.8)	$ (1,535.3)	$ (1,744.8)	$ (1,535.3)