Benefit Plans (Amounts Recorded in Accumulated Other Comprehensive Losses) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Net losses	$ (4,556)	$ (4,181)	$ (3,321)
Prior service cost	5	(24)	(31)
Net transition obligation	(4)	(4)	(5)
Deferred income taxes	726	563	541
Losses to be amortized	(3,829)	(3,646)	(2,816)
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Net losses	(3,718)	(3,438)	(2,624)
Prior service cost	3	(27)	(35)
Net transition obligation	(4)	(4)	(5)
Deferred income taxes	520	379	327
Losses to be amortized	(3,199)	(3,090)	(2,337)
Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Net losses	(63)	(41)	(80)
Prior service cost	2	3	4
Net transition obligation	0	0	0
Deferred income taxes	24	20	28
Losses to be amortized	(37)	(18)	(48)
Postemployment [Member]
Defined Benefit Plan Disclosure [Line Items]
Net losses	(775)	(702)	(617)
Prior service cost	0	0	0
Net transition obligation	0	0	0
Deferred income taxes	182	164	186
Losses to be amortized	$ (593)	$ (538)	$ (431)