Segment Information (Schedule Of Unallocated Items and Eliminations) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Share-based plans									$ (202)	$ (190)	$ (189)
Deferred compensation									(240)	(46)	(63)
Amortization of previously capitalized interest									(110)	(170)	(158)
Total	$ 3,030	$ 2,689	$ 2,535	$ 2,024	$ 2,183	$ 2,282	$ (419)	$ 1,788	10,278	5,834	7,443
Pension [Member]
Segment Reporting Information [Line Items]
Pension and Postretirement									(639)	(1,979)	(2,366)
Postretirement [Member]
Segment Reporting Information [Line Items]
Pension and Postretirement									(262)	(274)	(288)
Unallocated Items And Eliminations [Member]
Segment Reporting Information [Line Items]
Share-based plans									(77)	(66)	(76)
Deferred compensation									(240)	(46)	(63)
Amortization of previously capitalized interest									(98)	(94)	(90)
Eliminations and other unallocated items									(640)	(527)	(511)
Operating Loss Excluding Unallocated Pension and Postretirement Adjustments									(1,055)	(733)	(740)
Pension and Postretirement									1,308	370	(298)
Total									253	(363)	(1,038)
Unallocated Items And Eliminations [Member] | Pension [Member]
Segment Reporting Information [Line Items]
Pension and Postretirement									1,120	217	(421)
Unallocated Items And Eliminations [Member] | Postretirement [Member]
Segment Reporting Information [Line Items]
Pension and Postretirement									$ 188	$ 153	$ 123