Pension & Postretirement Expenses (Summary Of Net Periodic Pension And Net Postretirement Plan Expenses) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Sep. 30, 2016
Pension And Postretirement Plan Expenses [Line Items]
Service cost	$ 22	$ 27
Interest cost	50	60
Expected return on plan assets	(88)	(92)
Net amortization	40	43
Total	$ 24	$ 38
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)