Equity (Changes in Equity) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period		$ 9,420.2	$ 7,053.1	$ 7,213.4	$ 7,381.1
Net income		104.1	354.1	2,546.2	260.6
Other comprehensive income (loss)		176.8	(79.7)	161.8	2.3
Dividends on common stock		(207.0)	(186.2)	(601.0)	(546.7)
Dividends to noncontrolling interests		(7.9)	(8.4)	(19.5)	(23.2)
Share-based compensation		8.9	7.5	27.4	23.9
Treasury shares for stock option and award plans		17.8	32.0	25.5	62.8
Tax benefit of stock option and award plans	[1]		6.8		16.5
Spin-off of Versum				152.6
Cumulative change in accounting principle	[1]			8.8
Other equity transactions		(3.0)	1.0	(5.3)	2.9
Balance, end of period		$ 9,509.9	$ 7,180.2	$ 9,509.9	$ 7,180.2
Dividends per share (in dollars per share)		$ 0.95	$ 0.86	$ 2.76	$ 2.53
Air Products Shareholders' Equity [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period		$ 9,317.4	$ 6,916.6	$ 7,079.6	$ 7,249.0
Net income		101.9	346.8	2,531.7	237.1
Other comprehensive income (loss)		176.6	(79.0)	159.7	0.2
Dividends on common stock		(207.0)	(186.2)	(601.0)	(546.7)
Dividends to noncontrolling interests				0.0
Share-based compensation		8.9	7.5	27.4	23.9
Treasury shares for stock option and award plans		17.8	32.0	25.5	62.8
Tax benefit of stock option and award plans	[1]		6.8		16.5
Spin-off of Versum				186.5
Cumulative change in accounting principle	[1]			8.8
Other equity transactions		(3.2)	0.9	(5.8)	2.6
Balance, end of period		9,412.4	7,045.4	9,412.4	7,045.4
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period		102.8	136.5	133.8	132.1
Net income		2.2	7.3	14.5	23.5
Other comprehensive income (loss)		0.2	(0.7)	2.1	2.1
Dividends to noncontrolling interests		(7.9)	(8.4)	(19.5)	(23.2)
Spin-off of Versum				(33.9)
Other equity transactions		0.2	0.1	0.5	0.3
Balance, end of period		$ 97.5	$ 134.8	$ 97.5	$ 134.8

[1] Refer to Note 2, New Accounting Guidance, for information concerning the implementation and impact of new accounting guidance.