Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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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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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss).

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Comprehensive Income (Loss) (Reclassification Out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	$ (14)	$ (13)	$ (42)	$ (51)
Reclassifications, net of tax			(31)	(38)
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax			6	4
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Pension Benefits [Member] \| Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax impact	4	2	11	13
Reclassifications, net of tax	(10)	(11)	(31)	(38)
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Pension Benefits [Member] \| Actuarial Gains (Losses) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	(14)	(4)	(42)	(17)
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Pension Benefits [Member] \| Pension Settlement Cost [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax		(9)		(34)
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Postretirement Benefits Other Than Pensions (OPEB) [Member] \| Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	2	1	8	5
Tax impact			(2)	(1)
Reclassifications, net of tax	2	1	6	4
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Postretirement Benefits Other Than Pensions (OPEB) [Member] \| Prior-Service Credits (Costs) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	3	$ 1	7	6
Reclassification out of Accumulated Other Comprehensive Income [Member] \| Postretirement Benefits Other Than Pensions (OPEB) [Member] \| Actuarial Gains (Losses) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, pretax	$ (1)		$ 1	$ (1)