Income Taxes (Shareholder Activism-Related Costs) (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Shareholder activism-related costs	$ 86.3	$ 0.0	$ 0.0
Shareholder activism costs, net tax benefit	$ 14.6

Net tax benefit related to costs incurred as a result of a proxy contest for legal, proxy solicitation, executive separation costs, and other professional service fees.

No definition available.

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Namespace Prefix:	apd_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration