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, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income from continuing operations	$ 503.2	$ 488.0	$ 421.3	$ 347.5	$ 452.9	$ 430.7	$ 416.4	$ 155.6	$ 1,760.0	$ 1,455.6	$ 1,134.4
Net income from discontinued operations	0.0	0.0	0.0	0.0	0.0	43.2	0.0	(1.0)	0.0	42.2	1,866.0
Net Income Attributable to Air Products	$ 503.2	$ 488.0	$ 421.3	$ 347.5	$ 452.9	$ 473.9	$ 416.4	$ 154.6	$ 1,760.0	$ 1,497.8	$ 3,000.4
Weighted average common shares — Basic	220.7	220.6	220.2	219.9	219.6	219.5	219.4	218.9	220.3	219.3	218.0
Employee stock option and other award plans									1.3	1.5	1.8
Weighted average common shares — Diluted	222.1	221.9	221.4	221.0	220.9	220.9	220.8	220.4	221.6	220.8	219.8
Basic Earnings Per Common Share Attributable to Air Products
Basic earnings per share from continuing operations (in dollars per share)	$ 2.28	$ 2.21	$ 1.91	$ 1.58	$ 2.06	$ 1.96	$ 1.90	$ 0.71	$ 7.99	$ 6.64	$ 5.20
Basic earnings per share from discontinued operations (in dollars per share)	0	0	0	0	0	0.20	0	0	0	0.19	8.56
Basic Earnings Per Common Share Attributable to Air Products (in dollars per share)	2.28	2.21	1.91	1.58	2.06	2.16	1.90	0.71	7.99	6.83	13.76
Diluted Earnings Per Common Share Attributable to Air Products
Diluted earnings per share from continuing operations (in dollars per share)	2.27	2.20	1.90	1.57	2.05	1.95	1.89	0.70	7.94	6.59	5.16
Diluted earnings per share from discontinued operations (in dollars per share)	0	0	0	0	0	0.20	0	0	0	0.19	8.49
Diluted Earnings Per Common Share Attributable to Air Products (in dollars per share)	$ 2.27	$ 2.20	$ 1.90	$ 1.57	$ 2.05	$ 2.15	$ 1.89	$ 0.70	$ 7.94	$ 6.78	$ 13.65