Goodwill (Schedule of Goodwill by Segment) (Details) $ in Millions	9 Months Ended
Jun. 30, 2018 USD ($)
Goodwill [Roll Forward]
Goodwill, net, beginning balance	$ 721.5
Acquisitions	81.4
Currency translation	(8.8)
Goodwill, net, ending balance	794.1
Industrial Gases - Americas
Goodwill [Roll Forward]
Goodwill, net, beginning balance	163.7
Acquisitions	0.0
Currency translation	(1.4)
Goodwill, net, ending balance	162.3
Industrial Gases - EMEA
Goodwill [Roll Forward]
Goodwill, net, beginning balance	402.4
Acquisitions	30.8
Currency translation	(7.7)
Goodwill, net, ending balance	425.5
Industrial Gases - Asia
Goodwill [Roll Forward]
Goodwill, net, beginning balance	135.2
Acquisitions	39.8
Currency translation	0.3
Goodwill, net, ending balance	175.3
Industrial Gases - Global
Goodwill [Roll Forward]
Goodwill, net, beginning balance	20.2
Acquisitions	0.0
Currency translation	0.0
Goodwill, net, ending balance	20.2
Corporate and other
Goodwill [Roll Forward]
Goodwill, net, beginning balance	0.0
Acquisitions	10.8
Currency translation	0.0
Goodwill, net, ending balance	$ 10.8

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

+ Details

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

+ Details

Name:	us-gaap_GoodwillAcquiredDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

+ Details

Name:	us-gaap_GoodwillForeignCurrencyTranslationGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_GoodwillRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=apd_IndustrialGasesAmericasMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=apd_IndustrialGasesEmeaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=apd_IndustrialGasesAsiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=apd_IndustrialGasesGlobalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=us-gaap_CorporateAndOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: