Comprehensive Income (Loss) (Reclassification Out Of AOCI) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Costs [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax	$ (14)	$ (90)
Postretirement Costs [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax	3	5
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension Costs [Member] | Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	(18)	(120)
Tax impact	4	30
Reclassifications, net of tax	(14)	(90)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension Costs [Member] | Actuarial Gains (Losses) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	(18)	(17)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension Costs [Member] | Pension Settlement Cost [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax		(103)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Postretirement Costs [Member] | Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	4	6
Tax impact	(1)	(1)
Reclassifications, net of tax	3	5
Reclassification out of Accumulated Other Comprehensive Income [Member] | Postretirement Costs [Member] | Prior-Service Credits (Costs) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	7	8
Reclassification out of Accumulated Other Comprehensive Income [Member] | Postretirement Costs [Member] | Actuarial Gains (Losses) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	$ (3)	$ (2)