Earnings per Share (Schedule of Earnings per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended										12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018		Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017		Dec. 31, 2016	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2016
Earnings Per Share [Abstract]
Income from continuing operations	$ 452.9	$ 430.7		$ 416.4	$ 155.6	$ 474.2	$ 104.2	$ 304.4		$ 251.6	$ 1,455.6		$ 1,134.4		$ 1,099.5
Income (Loss) from discontinued operations	0.0	43.2	[1]	0.0	(1.0)	(5.5)	(2.3)	1,825.6	[2]	48.2	42.2	[1]	1,866.0	[2]	(468.4)
Net Income Attributable to Air Products	$ 452.9	$ 473.9		$ 416.4	$ 154.6	$ 468.7	$ 101.9	$ 2,130.0		$ 299.8	$ 1,497.8		$ 3,000.4		$ 631.1
Weighted average common shares — Basic											219.3		218.0		216.4
Employee stock option and other award plans											1.5		1.8		1.9
Weighted average common shares — Diluted	220.9	220.9		220.8	220.4	220.1	219.8	219.7		219.7	220.8		219.8		218.3
Basic Earnings Per Common Share Attributable to Air Products
Income from continuing operations (in dollars per share)	$ 2.06	$ 1.96		$ 1.90	$ 0.71	$ 2.17	$ 0.48	$ 1.40		$ 1.16	$ 6.64		$ 5.20		$ 5.08
Income (Loss) from discontinued operations (in dollars per share)	0	0.20		0	0	(0.02)	(0.01)	8.38		0.22	0.19		8.56		(2.16)
Net Income Attributable to Air Products (in dollars per share)	2.06	2.16		1.90	0.71	2.15	0.47	9.78		1.38	6.83		13.76		2.92
Diluted Earnings Per Common Share Attributable to Air Products
Income from continuing operations (in dollars per share)	2.05	1.95		1.89	0.70	2.15	0.47	1.39		1.15	6.59		5.16		5.04
Income (Loss) from discontinued operations (in dollars per share)	0	0.20		0	0	(0.02)	(0.01)	8.31		0.22	0.19		8.49		(2.15)
Net Income Attributable to Air Products (in dollars per share)	$ 2.05	$ 2.15		$ 1.89	$ 0.70	$ 2.13	$ 0.46	$ 9.70		$ 1.37	$ 6.78		$ 13.65		$ 2.89

[1] Primarily includes benefits resulting from the resolution of uncertain tax positions related to the disposition of our former European Homecare business and post-closing adjustments associated with the sale of PMD. For additional information, refer to Note 3, Discontinued Operations.

[2] Includes the after-tax gain on the sale of PMD. For additional information, see Note 3, Discontinued Operations.