Benefit Plans (Amounts Recorded in Accumulated Other Comprehensive Losses) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	$ (2,996)	$ (3,198)
Prior service (cost) credit	68	180
Deferred income taxes	760	1,179
Amounts recorded in accumulated other comprehensive losses	(2,168)	(1,839)
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	(2,591)	(2,493)
Prior service (cost) credit	(34)	(15)
Deferred income taxes	679	979
Amounts recorded in accumulated other comprehensive losses	(1,946)	(1,529)
Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	(327)	(612)
Prior service (cost) credit	108	195
Deferred income taxes	61	166
Amounts recorded in accumulated other comprehensive losses	(158)	(251)
Postemployment Retirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss	(78)	(93)
Prior service (cost) credit	(6)	0
Deferred income taxes	20	34
Amounts recorded in accumulated other comprehensive losses	$ (64)	$ (59)