Equity (Changes in Equity) (Details) - USD ($) $ / shares in Units, $ 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]
Balance, beginning of period	$ 7,261.1	$ 7,499.0	$ 7,213.4	$ 7,381.1
Net income (loss)	2,135.7	(465.5)	2,442.1	(93.5)
Other comprehensive income (loss)	223.0	164.7	(15.0)	82.0
Dividends on common stock	(206.9)	(185.8)	(394.0)	(360.5)
Dividends to noncontrolling interests	(7.5)	(6.3)	(11.7)	(14.8)
Share-based compensation	9.5	8.1	18.5	16.4
Treasury shares for stock option and award plans	7.9	32.8	7.6	30.8
Tax benefit of stock option and award plans		4.8	0.0	9.7
Spin-off of Versum			152.6
Cumulative change in accounting principle			8.8
Other equity transactions	(2.6)	1.3	(2.1)	1.9
Balance, end of period	$ 9,420.2	$ 7,053.1	$ 9,420.2	$ 7,053.1
Dividends per share (in dollars per share)	$ 0.95	$ 0.86	$ 1.81	$ 1.67
Air Products Shareholders' Equity [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	$ 7,161.5	$ 7,367.1	$ 7,079.6	$ 7,249.0
Net income (loss)	2,130.0	(473.3)	2,429.8	(109.7)
Other comprehensive income (loss)	218.0	161.9	(16.9)	79.2
Dividends on common stock	(206.9)	(185.8)	(394.0)	(360.5)
Dividends to noncontrolling interests			0.0	0.0
Share-based compensation	9.5	8.1	18.5	16.4
Treasury shares for stock option and award plans	7.9	32.8	7.6	30.8
Tax benefit of stock option and award plans		4.8	0.0	9.7
Spin-off of Versum			186.5
Cumulative change in accounting principle			8.8
Other equity transactions	(2.6)	1.0	(2.5)	1.7
Balance, end of period	9,317.4	6,916.6	9,317.4	6,916.6
Noncontrolling Interest [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	99.6	131.9	133.8	132.1
Net income (loss)	5.7	7.8	12.3	16.2
Other comprehensive income (loss)	5.0		1.9	2.8
Dividends on common stock			0.0	0.0
Dividends to noncontrolling interests	(7.5)	(6.3)	(11.7)	(14.8)
Share-based compensation			0.0	0.0
Treasury shares for stock option and award plans			0.0	0.0
Tax benefit of stock option and award plans			0.0	0.0
Spin-off of Versum			(33.9)
Other equity transactions	0.0	0.3	0.4	0.2
Balance, end of period	$ 102.8	$ 136.5	$ 102.8	$ 136.5