Variable Interest Entities (By Balance Sheet Items) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022	Sep. 30, 2022
Variable Interest Entity [Line Items]
Cash and cash items	$ 2,242.4		$ 2,242.4		$ 2,711.0
Trade receivables, net	1,714.7		1,714.7		1,794.4
Prepaid expenses	224.7		224.7		156.8
Other receivables and current assets	622.9		622.9		515.8
Plant and equipment, net	15,698.4		15,698.4		14,160.5
Other noncurrent assets	1,015.5		1,015.5		947.0
Total Assets	29,435.4		29,435.4		27,192.6
Payables and accrued liabilities	2,489.3		2,489.3		2,771.6
Accrued income taxes	128.2		128.2		135.2
Long-term debt – related party	688.6		688.6		652.0
Other noncurrent liabilities	1,096.3		1,096.3		1,099.1
Total Liabilities	14,745.2		14,745.2		13,490.2
Noncontrolling Interests	631.9		631.9		558.4
Shareholder loans	30.3	$ (2.4)	31.6	$ (1.7)
Non- controlling Interests
Variable Interest Entity [Line Items]
Shareholder loans	29.2	$ (2.8)	29.4	$ (2.9)
NEOM Green Hydrogen Company | Non- controlling Interests
Variable Interest Entity [Line Items]
Shareholder loans	29.0
Variable Interest Entity, Primary Beneficiary | NEOM Green Hydrogen Company
Variable Interest Entity [Line Items]
Cash and cash items	129.2		129.2		274.7
Trade receivables, net	0.0		0.0		1.3
Prepaid expenses	3.3		3.3		0.1
Other receivables and current assets	52.3		52.3		23.3
Plant and equipment, net	613.3		613.3		218.8
Other noncurrent assets	11.1		11.1		1.5
Total Assets	809.2		809.2		519.7
Payables and accrued liabilities	73.6		73.6		58.1
Accrued income taxes	0.4		0.4		0.0
Long-term debt – related party	476.7		476.7		447.3
Other noncurrent liabilities	3.0		3.0		1.4
Total Liabilities	553.7		553.7		506.8
Noncontrolling Interests	$ 2.6		$ 2.6		$ 30.0