Variable Interest Entities - NGHC Joint Venture Project Financing (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	6 Months Ended
	May 31, 2023	Mar. 31, 2025	Mar. 31, 2025	Sep. 30, 2024
Variable Interest Entity [Line Items]
Short-term borrowings		$ 773.2	$ 773.2	$ 83.5
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Company
Variable Interest Entity [Line Items]
Voting interest in joint venture			33.30%
Value of engineering, procurement, and construction agreement	$ 6,700.0
Short-term borrowings		64.4	$ 64.4	51.6
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Company | De-designated interest rate swap
Variable Interest Entity [Line Items]
Unrealized gain/loss on de-designated cash flow hedging instruments, before tax		11.5	(27.3)
Unrealized gain/loss on de-designated cash flow hedging instruments, attributable to noncontrolling interest, before tax		7.5	(17.7)
Unrealized gain/loss on de-designated cash flow hedging instruments attributable to Air Products, after tax		3.0	(7.3)
Variable Interest Entity, Primary Beneficiary | Nonrecourse | NEOM Green Hydrogen Company
Variable Interest Entity [Line Items]
Long-term debt, principal amount		4,300.0	4,300.0	3,300.0
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Project Financing, Primary | Nonrecourse | NEOM Green Hydrogen Company
Variable Interest Entity [Line Items]
Project financing maximum borrowing capacity		$ 6,100.0	$ 6,100.0
Amount of expected debt funding (percent)		73.00%	73.00%
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Project Financing, Working Capital | Nonrecourse | NEOM Green Hydrogen Company
Variable Interest Entity [Line Items]
Project financing maximum borrowing capacity		$ 500.0	$ 500.0
Variable Interest Entity, Primary Beneficiary | Saudi Riyal Loan Facility Variable-Rate 5.60% | NEOM Green Hydrogen Company
Variable Interest Entity [Line Items]
Short-term borrowings		$ 64.4	$ 64.4	$ 51.6
Interest rate, variable percentage		5.60%	5.60%	5.60%