Equity (Changes in Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Stockholders' Equity [Roll Forward]
Beginning balance	$ 10,185.5	$ 7,213.4
Net income	161.7	306.4
Other comprehensive income (loss)	153.7	(238.0)
Dividends on common stock	(208.0)	(187.1)
Dividends to noncontrolling interests	(7.7)	(4.2)
Share-based compensation	11.1	9.0
Treasury shares for stock option and award plans	19.9	(0.3)
Spin-off of Versum	0.0	152.6
Cumulative change in accounting principle	0.0	8.8
Other equity transactions	5.0	0.5
Ending balance	$ 10,321.2	$ 7,261.1
Dividends per share (in dollars per share)	$ 0.95	$ 0.86
Air Products Shareholders' Equity
Stockholders' Equity [Roll Forward]
Beginning balance	$ 10,086.2	$ 7,079.6
Net income	154.6	299.8
Other comprehensive income (loss)	151.8	(234.9)
Dividends on common stock	(208.0)	(187.1)
Share-based compensation	11.1	9.0
Treasury shares for stock option and award plans	19.9	(0.3)
Spin-off of Versum	0.0	186.5
Cumulative change in accounting principle	0.0	8.8
Other equity transactions	(0.3)	0.1
Ending balance	10,215.3	7,161.5
Non-controlling Interests
Stockholders' Equity [Roll Forward]
Beginning balance	99.3	133.8
Net income	7.1	6.6
Other comprehensive income (loss)	1.9	(3.1)
Dividends to noncontrolling interests	(7.7)	(4.2)
Spin-off of Versum	0.0	(33.9)
Cumulative change in accounting principle	0.0	0.0
Other equity transactions	5.3	0.4
Ending balance	$ 105.9	$ 99.6