Postretirement Plans (Components Of Net Postretirement Benefits Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Postretirement Benefit Plans [Line Items]
Net postretirement expense	$ 2	$ 49	$ 127
Postretirement Plans [Member]
Postretirement Benefit Plans [Line Items]
Service cost	1	1	1
Interest cost	5	6	6
Net amortization	(18)	(19)	(19)
Net postretirement expense	$ (12)	$ (12)	$ (12)