Variable Interest Entities- NGHC Joint Venture (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	May 31, 2023	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2024
Variable Interest Entity [Line Items]
Short-term borrowings		$ 83.5	$ 83.5	$ 259.5
Operating lease right-of-use assets, net		1,047.7	1,047.7	974.0
Use of cash for payments on operating leases			$ 154.6	337.8	$ 128.0
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Company
Variable Interest Entity [Line Items]
Voting interest in joint venture			33.33333%
Value of engineering, procurement, and construction agreement	$ 6,700.0
Short-term borrowings		51.6	$ 51.6	0.0
Operating lease right-of-use assets, net		233.9	233.9	228.9
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Company | Land
Variable Interest Entity [Line Items]
Lessee, operating lease, term						50 years
Operating lease right-of-use assets, net		223.0	$ 223.0
Use of cash for payments on operating leases		$ 209.0		209.0
Lessee, operating lease, years additional payments due after commencement		30 years	30 years
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Company | De-Designated Interest Rate Swaps
Variable Interest Entity [Line Items]
Unrealized gain (loss) on de-designated cash flow hedging instruments, before tax		$ 16.3
Unrealized gain (loss) on de-designated cash flow hedging instruments attributable to parent after tax		4.3
Unrealized gain (loss) on de-designated cash flow hedging instruments attributable to noncontrolling interest, before tax		(10.6)
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Company | Nonrecourse
Variable Interest Entity [Line Items]
Long-term and short-term debt, combined amount		3,323.4	$ 3,323.4	$ 1,364.8
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Company | NEOM Green Hydrogen Project Financing, Primary | Nonrecourse
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 Company | NEOM Green Hydrogen Project Financing, Working Capital | Nonrecourse
Variable Interest Entity [Line Items]
Project financing, maximum borrowing capacity		$ 500.0	$ 500.0
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Company | Saudi Riyal Loan Facility Variable-Rate 6.21%
Variable Interest Entity [Line Items]
Short-term borrowings		$ 51.6	$ 51.6
Interest rate, variable percentage		6.21%	6.21%