Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 10,185.5	$ 7,213.4
Other comprehensive income (loss) before reclassifications	126.9
Amounts reclassified from AOCL	26.8
Total Other Comprehensive Income (Loss)	153.7	(238.0)
Amount attributable to noncontrolling interests	1.9	(3.1)
Ending balance	10,321.2	$ 7,261.1
Derivatives qualifying as hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(53.1)
Other comprehensive income (loss) before reclassifications	(9.5)
Amounts reclassified from AOCL	0.8
Total Other Comprehensive Income (Loss)	(8.7)
Amount attributable to noncontrolling interests	0.0
Ending balance	(61.8)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(787.1)
Other comprehensive income (loss) before reclassifications	136.4
Amounts reclassified from AOCL	3.1
Total Other Comprehensive Income (Loss)	139.5
Amount attributable to noncontrolling interests	1.9
Ending balance	(649.5)
Pension and postretirement benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,007.2)
Other comprehensive income (loss) before reclassifications	0.0
Amounts reclassified from AOCL	22.9
Total Other Comprehensive Income (Loss)	22.9
Amount attributable to noncontrolling interests	0.0
Ending balance	(984.3)
AOCL attributable to Air Products
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,847.4)
Ending balance	$ (1,695.6)