Variable Interest Entities (NGHC Joint Venture Project Financing) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	May 31, 2023	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Sep. 30, 2025
Variable Interest Entity [Line Items]
Long-term debt proceeds			$ 644.0	$ 3,978.2
Short-term borrowings			$ 126.7		$ 34.7
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Voting interest in joint venture			33.33%
Value of engineering, procurement, and construction agreement	$ 6,700.0
Short-term borrowings			$ 90.1		24.0
Variable Interest Entity, Primary Beneficiary | Nonrecourse
Variable Interest Entity [Line Items]
Total principal borrowings			5,500.0		4,900.0
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Project Financing, Primary | Nonrecourse
Variable Interest Entity [Line Items]
Project financing maximum borrowing capacity			$ 6,100.0
Amount of expected debt funding (percent)			69.00%
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Project Financing, Working Capital | Nonrecourse
Variable Interest Entity [Line Items]
Project financing maximum borrowing capacity			$ 500.0
Variable Interest Entity, Primary Beneficiary | 2026 Facilities | Nonrecourse
Variable Interest Entity [Line Items]
Long-term debt proceeds			543.0
Variable Interest Entity, Primary Beneficiary | U.S. Dollar Variable Rate Facility | Nonrecourse
Variable Interest Entity [Line Items]
Long-term debt proceeds			$ 260.0
Interest rate, stated percentage			4.90%
Variable Interest Entity, Primary Beneficiary | Saudi Riyal Facility Stated-Rate 2.00% | Nonrecourse
Variable Interest Entity [Line Items]
Long-term debt proceeds			$ 250.0
Interest rate, stated percentage			2.00%
Variable Interest Entity, Primary Beneficiary | Saudi Riyal Loan Facility Variable-Rate 5.40% | Nonrecourse
Variable Interest Entity [Line Items]
Short-term borrowings			$ 90.0		$ 24.0
Interest rate, variable percentage			5.40%
Variable Interest Entity, Primary Beneficiary | De-designated interest rate swap
Variable Interest Entity [Line Items]
Unrealized gain (loss) on de-designated cash flow hedging instruments, before tax		$ (0.3)		27.0
Unrealized gain (loss) on de-designated cash flow hedging instruments, amount attributable to noncontrolling interest, before tax		(0.1)		17.6
Unrealized gain (loss) on de-designated cash flow hedging instruments, amount attributable to Air Products, after tax		$ (0.1)		$ 7.2