Summary by Quarter (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended																	12 Months Ended
		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015	Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2015
Quarterly Financial Information Disclosure [Abstract]
Sales		$ 2,203.1		$ 2,121.9		$ 1,980.1		$ 1,882.5		$ 1,945.5		$ 1,914.5		$ 1,777.4		$ 1,866.3			$ 8,187.6		$ 7,503.7		$ 7,824.3
Gross profit	[1]	657.8		635.7		576.3		564.4		598.0		594.3		564.4		570.4			2,434.2		2,327.1
Business separation costs		0.0	[2]	0.0	[2]	0.0	[2]	30.2	[2]	21.7	[2]	9.5	[2]	7.4	[2]	12.0	[2]		30.2	[2]	50.6	[2]	7.5
Business restructuring and cost reduction actions		48.4	[3]	42.7	[3]	10.3	[3]	50.0	[3]	10.6	[3]	13.2	[3]	10.7	[3]	0.0	[3]		151.4	[3]	34.5	[3]	180.1
Pension settlement loss		0.9	[4]	5.5	[4]	4.1	[4]	0.0	[4]	2.1	[4]	1.0	[4]	2.0	[4]	0.0	[4]		10.5	[4]	5.1	[4]	19.3
Goodwill and intangible asset impairment charge		0.0	[5]	162.1	[5]	0.0	[5]	0.0	[5]										162.1	[5]	0.0		0.0
Gain on land sale		12.2	[6]	0.0	[6]	0.0	[6]	0.0	[6]									$ 33.6	12.2	[6]
Operating income		455.7	[1]	252.6	[1]	391.2	[1]	328.1	[1]	391.0	[1]	394.6	[1]	371.6	[1]	372.5	[1]		1,427.6	[1]	1,529.7	[1]	1,233.2
Equity affiliates' income (loss)		44.8		(36.9)	[7]	34.2		38.0		39.3		42.1		32.3		33.3			80.1	[7]	147.0		152.3
Loss on extinguishment of debt										6.9	[8]	0.0	[8]	0.0	[8]	0.0	[8]		0.0		6.9	[8]	16.6
Income tax provision (benefit)		(1.3)	[9]	89.3		94.5		78.4		96.8	[10]	145.9	[10]	93.5	[10]	96.4			260.9	[9]	432.6	[10]	300.2
Net income (loss)		475.0		104.1		2,135.7		306.4		400.9		354.1		(465.5)		372.0			3,021.2		661.5		1,317.6
Income from continuing operations		474.2		104.2		304.4		251.6		289.4		250.3		278.9		280.9			1,134.4		1,099.5		933.3
Income (Loss) from discontinued operations		(5.5)		(2.3)		1,825.6	[11]	48.2		104.6		96.5		(752.2)		82.7			1,866.0	[11]	(468.4)		344.6
Net income (loss) attributable to Air Products		$ 468.7		$ 101.9		$ 2,130.0		$ 299.8		$ 394.0		$ 346.8		$ (473.3)		$ 363.6			$ 3,000.4		$ 631.1		$ 1,277.9
Basic Earnings Per Common Share Attributable to Air Products
Income from continuing operations (in dollars per share)		$ 2.17		$ 0.48		$ 1.40		$ 1.16		$ 1.33		$ 1.16		$ 1.29		$ 1.30			$ 5.20		$ 5.08		$ 4.34
Income (Loss) from discontinued operations (in dollars per share)		(0.02)		(0.01)		8.38		0.22		0.48		0.44		(3.48)		0.38			8.56		(2.16)		1.61
Net Income Attributable to Air Products (in dollars per share)		2.15		0.47		9.78		1.38		1.81		1.60		(2.19)		1.68			13.76		2.92		5.95
Diluted Earnings Per Common Share Attributable to Air Products
Income from continuing operations (in dollars per share)		2.15		0.47		1.39		1.15		1.32		1.15		1.28		1.29			5.16		5.04		4.29
Income (Loss) from discontinued operations (in dollars per share)		(0.02)		(0.01)		8.31		0.22		0.48		0.44		(3.45)		0.38			8.49		(2.15)		1.59
Net Income Attributable to Air Products (in dollars per share)		2.13		0.46		9.70		1.37		1.80		1.59		(2.17)		1.67			13.65		2.89		5.88
Dividends declared per common share		0.95		0.95		0.95		0.86		0.86		0.86		0.86		0.81			$ 3.71		$ 3.39		$ 3.20
Market price per common share - High		152.26		147.66		149.46		150.45		146.82		141.53		136.88		133.78
Market price per common share - Low		$ 141.88		$ 134.09		$ 133.63		$ 129.00		$ 127.72		$ 124.78		$ 106.63		$ 117.80
Change in Accounting Estimate [Line Items]
Operating income		$ 455.7	[1]	$ 252.6	[1]	$ 391.2	[1]	$ 328.1	[1]	$ 391.0	[1]	$ 394.6	[1]	$ 371.6	[1]	$ 372.5	[1]		$ 1,427.6	[1]	$ 1,529.7	[1]	$ 1,233.2
Contracts accounted for under percentage of completion
Quarterly Financial Information Disclosure [Abstract]
Operating income																			27.0		20.0
Change in Accounting Estimate [Line Items]
Operating income																			$ 27.0		$ 20.0

[1] Changes in estimates on projects accounted for under the percentage of completion method favorably impacted income by approximately $27 in fiscal year 2017 and $20 in fiscal year 2016, primarily during the fourth quarter. For additional information, see Note 1, Major Accounting Policies (Revenue Recognition).

[2] For additional information, see Note 4, Materials Technologies Separation.

[3] For additional information, see Note 5, Business Restructuring and Cost Reduction Actions.

[4] For additional information, see Note 16, Retirement Benefits.

[5] For additional information, see Note 10, Goodwill, and Note 11, Intangible Assets.

[6] The gain is reflected on the consolidated income statements in "Other income (expense), net." For additional information, see Note 23, Supplemental Information.

[7] Includes the impact of an other-than-temporary impairment of an investment in an equity affiliate. For additional information, see Note 8, Summarized Financial Information of Equity Affiliates.

[8] For additional information, see Note 15, Debt.

[9] Includes the impact of a tax election benefit related to a non-U.S. subsidiary. For additional information, see Note 22, Income Taxes.

[10] Includes income tax expense for tax costs associated with business separation. For additional information, see Note 4, Materials Technologies Separation.

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