Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 7,079.6
Other comprehensive loss before reclassifications	(291.0)
Amounts reclassified from AOCL	53.0
Net current period other comprehensive income (loss)	(238.0)	$ (82.7)
Spin-off of Versum	11.5
Amount attributable to noncontrolling interests	(3.1)	$ 0.0
Ending balance	7,161.5
Net loss on derivatives qualifying as hedges [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(65.0)
Other comprehensive loss before reclassifications	(9.8)
Amounts reclassified from AOCL	25.6
Net current period other comprehensive income (loss)	15.8
Spin-off of Versum	0.2
Amount attributable to noncontrolling interests	0.0
Ending balance	(49.0)
Foreign currency translation adjustments [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(949.3)
Other comprehensive loss before reclassifications	(281.2)
Amounts reclassified from AOCL	0.0
Net current period other comprehensive income (loss)	(281.2)
Spin-off of Versum	6.0
Amount attributable to noncontrolling interests	(3.1)
Ending balance	(1,221.4)
Pension and postretirement benefits [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,374.0)
Other comprehensive loss before reclassifications	0.0
Amounts reclassified from AOCL	27.4
Net current period other comprehensive income (loss)	27.4
Spin-off of Versum	5.3
Amount attributable to noncontrolling interests	0.0
Ending balance	(1,341.3)
AOCL attributable to Air Products [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(2,388.3)
Ending balance	$ (2,611.7)