Comprehensive Income (Loss) (Reclassification Out Of Accumulated Other Comprehensive) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax			$ (233)	$ (31)
Postretirement Costs [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax			10	6
Reclassification out of Accumulated Other Comprehensive Loss [Member] | Pension Benefits [Member] | Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	$ (29)	$ (14)	(296)	(42)
Tax impact	4	4	63	11
Reclassifications, net of tax	(25)	(10)	(233)	(31)
Reclassification out of Accumulated Other Comprehensive Loss [Member] | Pension Benefits [Member] | Actuarial Gains (Losses) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	(29)	(14)	(76)	(42)
Reclassification out of Accumulated Other Comprehensive Loss [Member] | Pension Benefits [Member] | One-Time Gain (Loss) On disposal [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax			(61)
Reclassification out of Accumulated Other Comprehensive Loss [Member] | Pension Benefits [Member] | Pension Settlement Cost [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax			(159)
Reclassification out of Accumulated Other Comprehensive Loss [Member] | Postretirement Costs [Member] | Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	7	2	13	8
Tax impact	(2)		(3)	(2)
Reclassifications, net of tax	5	2	10	6
Reclassification out of Accumulated Other Comprehensive Loss [Member] | Postretirement Costs [Member] | Prior-Service Credits (Costs) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	8	3	24	7
Reclassification out of Accumulated Other Comprehensive Loss [Member] | Postretirement Costs [Member] | Actuarial Gains (Losses) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	$ (1)	$ (1)	(4)	$ 1
Reclassification out of Accumulated Other Comprehensive Loss [Member] | Postretirement Costs [Member] | One-Time Gain (Loss) On disposal [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax			$ (7)