Accumulated Other Comprehensive Loss (Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			$ 7,079.6
Other comprehensive income (loss) before reclassifications	$ 138.0		(153.0)
Amounts reclassified from AOCL	85.0		138.0
Net current period other comprehensive income (loss)	223.0	$ 164.7	(15.0)	$ 82.0
Spin-off of Versum			11.5
Amount attributable to noncontrolling interests	5.0	$ 2.8	1.9	$ 2.8
Ending balance	9,317.4		9,317.4
Net loss on derivatives qualifying as hedges [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(49.0)		(65.0)
Other comprehensive income (loss) before reclassifications	(15.4)		(25.2)
Amounts reclassified from AOCL	5.8		31.4
Net current period other comprehensive income (loss)	(9.6)		6.2
Spin-off of Versum			0.2
Amount attributable to noncontrolling interests	(0.1)		(0.1)
Ending balance	(58.5)		(58.5)
Foreign currency translation adjustments [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,221.4)		(949.3)
Other comprehensive income (loss) before reclassifications	149.6		(131.6)
Amounts reclassified from AOCL	49.1		49.1
Net current period other comprehensive income (loss)	198.7		(82.5)
Spin-off of Versum			6.0
Amount attributable to noncontrolling interests	5.0		1.9
Ending balance	(1,027.7)		(1,027.7)
Pension and postretirement benefits [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,341.3)		(1,374.0)
Other comprehensive income (loss) before reclassifications	3.8		3.8
Amounts reclassified from AOCL	30.1		57.5
Net current period other comprehensive income (loss)	33.9		61.3
Spin-off of Versum			5.3
Amount attributable to noncontrolling interests	0.1		0.1
Ending balance	(1,307.5)		(1,307.5)
AOCL attributable to Air Products [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(2,611.7)		(2,388.3)
Ending balance	$ (2,393.7)		$ (2,393.7)