Postretirement Plans (Components Of Net Postretirement Benefits Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Postretirement Benefit Plans [Line Items]
Net postretirement expense	$ 95	$ 153	$ 142
Postretirement Plans [Member]
Postretirement Benefit Plans [Line Items]
Service cost	1	1	1
Interest cost	8	9	11
Net amortization	(21)	(22)	(21)
Net postretirement expense	$ (12)	$ (12)	$ (9)