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, 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
Quarterly Financial Information Disclosure [Abstract]
Sales		$ 2,283.2	$ 2,224.0		$ 2,187.7	$ 2,224.0		$ 2,298.9		$ 2,259.0	$ 2,155.7		$ 2,216.6		$ 8,918.9		$ 8,930.2		$ 8,187.6
Gross profit		792.4	758.0		713.0	651.0	[1]	733.1	[2]	713.6	649.2		644.8		2,914.4	[1]	2,740.7	[2]
Cost reduction and asset actions		0.0	25.5		0.0	0.0									25.5		0.0		151.4
Gain on exchange of equity affiliate investments	$ 29.1	0.0	29.1		0.0	0.0									29.1		0.0		0.0
Operating income		603.2	569.7		516.5	455.0		533.7		515.8	455.4		460.7		2,144.4		1,965.6		1,440.0
Equity affiliates' income		59.9	56.4		46.2	52.9		59.2		58.1	43.7		13.8		215.4		174.8		80.1
Pension settlement loss		0.0	0.0		5.0	0.0		43.7		0.0	0.0		0.0		5.0		43.7
Income tax provision		131.2	109.3	[3]	107.5	132.1	[3]	69.2	[3],[4]	107.1	56.2	[4]	291.8	[3]	480.1	[3]	524.3	[3],[4]	260.9
Income from continuing operations		518.7	500.2		433.5	357.0		459.7		444.7	423.6		162.7		1,809.4		1,490.7		1,155.2
Income from discontinued operations, net of tax		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		518.7	500.2		433.5	357.0		459.7		487.9	423.6		161.7		1,809.4		1,532.9		3,021.2
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
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
Weighted Average Common Shares - Basic (in millions)		220.7	220.6		220.2	219.9		219.6		219.5	219.4		218.9		220.3		219.3		218.0
Weighted Average Common Shares - Diluted (in millions)		222.1	221.9		221.4	221.0		220.9		220.9	220.8		220.4		221.6		220.8		219.8
Dividends declared per common share		$ 1.16	$ 1.16		$ 1.16	$ 1.10		$ 1.10		$ 1.10	$ 1.10		$ 0.95		$ 4.58		$ 4.25		$ 3.71
Facility closure						$ 0.0									$ 29.0		$ 0.0		$ 0.0
Discrete net tax expense related to Tax Act															43.8		180.6
Tax benefit from restructuring of foreign subsidiaries																	(35.7)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in cost of sales															$ (5,975.5)		(6,189.5)		$ (5,751.5)
Change in Inventory Valuation Method
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in cost of sales								$ 24.1									$ 24.1

[1] Includes the impact of a facility closure charge of $29.0 resulting from the government enforced shutdown of a customer. Refer to Note 24, Supplemental Information, for additional information.

[2] Includes the impact of a benefit of $24.1 for the change in inventory valuation method for our United States industrial gas inventories. Refer to Note 1, Major Accounting Policies, for additional information.

[3] Our income tax provision for fiscal years 2019 and 2018 reflects impacts from the U.S. Tax Cuts and Jobs Act (the "Tax Act"). Refer to Note 23, Income Taxes, for additional information. Fiscal year 2019 includes a discrete net income tax expense of $43.8, primarily recorded in the first quarter to finalize our estimates of the impacts of the Tax Act. Fiscal year 2018 includes a discrete net income tax expense of $180.6, primarily recorded in the first quarter for our initial estimates of the impacts of the Tax Act.

[4] Includes an income tax benefit of $35.7, net of reserves for uncertain tax positions, resulting from the restructuring of several foreign subsidiaries, primarily during the second quarter.