Debt - Schedule of Receivables Facility (Details) - Energy Services - Receivables Facility - Energy Services Receivables Facility - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Short-term Debt [Line Items]
Trade receivables transferred to ESFC during the year	$ 1,046	$ 1,373	$ 1,280
Trade receivables transferred to ESFC during the year	182	179	193
ESFC trade receivables - end of year	50	55	$ 65
Outstanding balance of trade receivables sold	$ 19	$ 46