Equity (Changes in Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stockholders' Equity [Roll Forward]
Beginning balance	$ 10,693.2	$ 9,420.2	$ 10,185.5	$ 7,213.4
Net income	487.9	104.1	1,073.2	2,546.2
Other comprehensive income (loss)	(357.0)	176.8	(40.8)	161.8
Dividends on common stock	(241.2)	(207.0)	(690.3)	(601.0)
Dividends to noncontrolling interests	(15.4)	(7.9)	(26.0)	(19.5)
Share-based compensation	7.9	8.9	29.7	27.4
Treasury shares for stock option and award plans	5.4	17.8	45.5	25.5
Spin-off of Versum			0.0	(152.6)
Cumulative change in accounting principle			0.0	8.8
Lu'An joint venture	227.4		227.4
Other equity transactions	1.8	(3.0)	5.8	(5.3)
Ending balance	$ 10,810.0	$ 9,509.9	$ 10,810.0	$ 9,509.9
Dividends per share (in dollars per share)	$ 1.10	$ 0.95	$ 3.15	$ 2.76
Air Products Shareholders' Equity
Stockholders' Equity [Roll Forward]
Beginning balance	$ 10,580.8	$ 9,317.4	$ 10,086.2	$ 7,079.6
Net income	473.9	101.9	1,044.9	2,531.7
Other comprehensive income (loss)	(342.5)	176.6	(30.4)	159.7
Dividends on common stock	(241.2)	(207.0)	(690.3)	(601.0)
Share-based compensation	7.9	8.9	29.7	27.4
Treasury shares for stock option and award plans	5.4	17.8	45.5	25.5
Spin-off of Versum			0.0	(186.5)
Cumulative change in accounting principle			0.0	8.8
Other equity transactions	1.7	(3.2)	0.4	(5.8)
Ending balance	10,486.0	9,412.4	10,486.0	9,412.4
Non-controlling Interests
Stockholders' Equity [Roll Forward]
Beginning balance	112.4	102.8	99.3	133.8
Net income	14.0	2.2	28.3	14.5
Other comprehensive income (loss)	(14.5)	0.2	(10.4)	2.1
Dividends to noncontrolling interests	(15.4)	(7.9)	(26.0)	(19.5)
Spin-off of Versum			0.0	(33.9)
Lu'An joint venture	227.4		227.4
Other equity transactions	0.1	0.2	5.4	0.5
Ending balance	$ 324.0	$ 97.5	$ 324.0	$ 97.5