Summary by Quarter (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended								12 Months Ended
	May 01, 2019	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Sales		$ 2,320.1	$ 2,065.2	$ 2,216.3	$ 2,254.7	$ 2,283.2	$ 2,224.0	$ 2,187.7	$ 2,224.0	$ 8,856.3		$ 8,918.9		$ 8,930.2
Gross profit		753.6	720.3	756.2	768.1	792.4	758.0	713.0	651.0	2,998.2		2,914.4
Cost reduction actions						0.0	25.5	0.0	0.0	0.0		25.5		0.0
Gain on exchange of equity affiliate investments	$ 29.1					0.0	29.1	0.0	0.0	0.0		29.1		0.0
Company headquarters relocation income (expense)		0.0	0.0	33.8	0.0					33.8		0.0		0.0
Operating income		560.2	539.2	577.2	561.0	603.2	569.7	516.5	455.0	2,237.6		2,144.4		1,965.6
Equity affiliates' income		67.2	51.2	88.2	58.2	59.9	56.4	46.2	52.9	264.8		215.4		174.8
Pension settlement loss						0.0	0.0	5.0	0.0			5.0
Income tax provision		99.9	109.3	148.5	120.7	131.2	109.3	107.5	132.1	478.4		480.1		524.3
Income from continuing operations		494.7	457.1	504.7	488.9	518.7	500.2	433.5	357.0	1,945.4		1,809.4		1,490.7
Income (loss) from discontinued operations, net of tax		0.0	0.0	(14.3)	0.0	0.0	0.0	0.0	0.0	(14.3)		0.0		42.2
Net income		494.7	457.1	490.4	488.9	518.7	500.2	433.5	357.0	1,931.1		1,809.4		1,532.9
Net Income Attributable to Air Products
Net income from continuing operations		486.8	446.5	492.1	475.6	503.2	488.0	421.3	347.5	1,901.0		1,760.0		1,455.6
Net (loss) income from discontinued operations		0.0	0.0	(14.3)	0.0	0.0	0.0	0.0	0.0	(14.3)		0.0		42.2
Net Income Attributable to Air Products		$ 486.8	$ 446.5	$ 477.8	$ 475.6	$ 503.2	$ 488.0	$ 421.3	$ 347.5	$ 1,886.7		$ 1,760.0		$ 1,497.8
Per Share Data
Basic EPS from continuing operations (in dollars per share)		$ 2.20	$ 2.02	$ 2.22	$ 2.15	$ 2.28	$ 2.21	$ 1.91	$ 1.58	$ 8.59	[1]	$ 7.99	[1]	$ 6.64	[1]
Basic EPS from discontinued operations (in dollars per share)		0	0	(0.06)	0	0	0	0	0	(0.06)	[1]	0	[1]	0.19	[1]
Basic EPS Attributable to Air Products (in dollars per share)		2.20	2.02	2.16	2.15	2.28	2.21	1.91	1.58	8.53	[1]	7.99	[1]	6.83	[1]
Diluted EPS from continuing operations (in dollars per share)		2.19	2.01	2.21	2.14	2.27	2.20	1.90	1.57	8.55	[1]	7.94	[1]	6.59	[1]
Diluted EPS from discontinued operations (in dollars per share)		0	0	(0.06)	0	0	0	0	0	(0.06)	[1]	0	[1]	0.19	[1]
Diluted EPS Attributable to Air Products (in dollars per share)		$ 2.19	$ 2.01	$ 2.15	$ 2.14	$ 2.27	$ 2.20	$ 1.90	$ 1.57	$ 8.49	[1]	$ 7.94	[1]	$ 6.78	[1]
Weighted Average Common Shares (in millions)
Basic		221.3	221.2	221.2	220.9	220.7	220.6	220.2	219.9	221.2		220.3		219.3
Diluted		222.6	222.4	222.3	222.2	222.1	221.9	221.4	221.0	222.3		221.6		220.8
Dividends declared per common share		$ 1.34	$ 1.34	$ 1.34	$ 1.16	$ 1.16	$ 1.16	$ 1.16	$ 1.10	$ 5.18		$ 4.58		$ 4.25
Proportionate share of accumulated dividend distribution taxes released per the India Finance Act			$ 33.8							$ 33.8
Income tax provision related to estimated withholding taxes on future dividends			$ 20.3							20.3
Facility closure									$ 29.0	$ 0.0		$ 29.0		$ 0.0
Discrete net tax expense related to Tax Act												$ 43.8		$ 180.6

[1] Earnings per share ("EPS") is calculated independently for each component and may not sum to total EPS due to rounding.