Debt - Schedule of Receivables Facility (Details) - Energy Services - Receivables Facility - Energy Services Receivables Facility - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Short-term Debt [Line Items]
Trade receivables transferred to ESFC during the year	$ 1,353,000,000	$ 1,046,000,000	$ 1,373,000,000
ESFC trade receivables sold to the bank during the year	308,000,000	182,000,000	179,000,000
ESFC trade receivables - end of year	61,000,000	50,000,000	$ 55,000,000
Outstanding balance of trade receivables sold	$ 0	$ 19,000,000