Postretirement Plans (Components Of Net Postretirement Benefits Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Postretirement Benefit Plans [Line Items]
Net postretirement expense	$ 49	$ 127	$ 95
Postretirement Plans [Member]
Postretirement Benefit Plans [Line Items]
Service cost	1	1	1
Interest cost	6	6	8
Net amortization	(19)	(19)	(21)
Net postretirement expense	$ (12)	$ (12)	$ (12)