Pension & Postretirement Expenses (Summary Of Net Periodic Pension And Net Postretirement Plan Expenses) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015	Sep. 30, 2016
Pension And Postretirement Plan Expenses [Line Items]
Service cost	$ 23	$ 27	$ 45	$ 54
Interest cost	49	61	99	121
Expected return on plan assets	(88)	(92)	(176)	(184)
Net amortization	41	42	81	85
Total	$ 25	$ 38	$ 49	$ 76
Change in Assumptions for Pension Plans [Member] | Scenario, Forecast [Member]
Pension And Postretirement Plan Expenses [Line Items]
Discount rate used to measure service cost for pension expense					4.60%
Discount rate used to measure interest cost for pension expense					3.50%
Defined benefit plan, assumptions used calculating net periodic benefit cost, discount rate					4.35%
Change in estimated service cost and interest cost for pension expense					$ (38)
Change in estimated service cost and interest cost for pension expense per share					$ (0.04)