Comprehensive Loss (Reclassification Out Of AOCI) (Details) - Reclassification out of Accumulated Other Comprehensive Income [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits [Member] \| Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	$ (115)	$ (65)	$ (113)
Tax impact	26	18	43
Reclassifications, net of tax	(89)	(47)	(70)
Pension Benefits [Member] \| Actuarial Gains (Losses) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	(58)	(24)	(30)
Pension Benefits [Member] \| Pension Settlement Cost [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	(57)	(41)	(83)
Reclassifications, net of tax	(43)	31	51
Postretirement Costs [Member] \| Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	15	6	9
Tax impact	(2)	(2)	(3)
Reclassifications, net of tax	13	4	6
Postretirement Costs [Member] \| Prior-Service Credits (Costs) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	11	9	$ 9
Postretirement Costs [Member] \| Actuarial Gains (Losses) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	$ 4	$ (3)

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Amount before tax of reclassification adjustments of other comprehensive income (loss).

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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