Equity (Changes in Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Stockholders' Equity [Roll Forward]
Beginning balance	$ 10,321.2	$ 7,261.1	$ 10,185.5	$ 7,213.4
Net income	423.6	2,135.7	585.3	2,442.1
Other comprehensive income (loss)	162.5	223.0	316.2	(15.0)
Dividends on common stock	(241.1)	(206.9)	(449.1)	(394.0)
Dividends to noncontrolling interests	(2.9)	(7.5)	(10.6)	(11.7)
Share-based compensation	10.7	9.5	21.8	18.5
Treasury shares for stock option and award plans	20.2	7.9	40.1	7.6
Spin-off of Versum			0.0	(152.6)
Cumulative change in accounting principle			0.0	8.8
Other equity transactions	(1.0)	(2.6)	4.0	(2.1)
Ending balance	$ 10,693.2	$ 9,420.2	$ 10,693.2	$ 9,420.2
Dividends per share (in dollars per share)	$ 1.10	$ 0.95	$ 2.05	$ 1.81
Air Products Shareholders' Equity
Stockholders' Equity [Roll Forward]
Beginning balance	$ 10,215.3	$ 7,161.5	$ 10,086.2	$ 7,079.6
Net income	416.4	2,130.0	571.0	2,429.8
Other comprehensive income (loss)	160.3	218.0	312.1	(16.9)
Dividends on common stock	(241.1)	(206.9)	(449.1)	(394.0)
Share-based compensation	10.7	9.5	21.8	18.5
Treasury shares for stock option and award plans	20.2	7.9	40.1	7.6
Spin-off of Versum			0.0	(186.5)
Cumulative change in accounting principle			0.0	8.8
Other equity transactions	(1.0)	(2.6)	(1.3)	(2.5)
Ending balance	10,580.8	9,317.4	10,580.8	9,317.4
Non-controlling Interests
Stockholders' Equity [Roll Forward]
Beginning balance	105.9	99.6	99.3	133.8
Net income	7.2	5.7	14.3	12.3
Other comprehensive income (loss)	2.2	5.0	4.1	1.9
Dividends to noncontrolling interests	(2.9)	(7.5)	(10.6)	(11.7)
Spin-off of Versum			0.0	(33.9)
Other equity transactions	0.0	0.0	5.3	0.4
Ending balance	$ 112.4	$ 102.8	$ 112.4	$ 102.8