Accumulated Other Comprehensive Income (Loss) - Components of Accumulated Other Comprehensive Income, Net of Tax (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Deferred Taxes
Balance	$ (43)	$ (144)	$ (39)	$ (160)
Changes in value	(2)	156	(5)	171
Amounts reclassified to earnings	(2)	(17)	(3)	(16)
Balance	(47)	(5)	(47)	(5)
Total
Balance	5,206	9,418	5,960	11,531
Changes in value	9	(548)	18	(598)
Amounts reclassified to earnings	3	60	7	57
Balance	4,904	8,517	4,904	8,517
Pension and Other Postretirement Liabilities
Before Tax
Balance	(1,084)	(613)	(1,102)	(560)
Changes in value	11	(721)	24	(770)
Amounts reclassified to earnings	5	77	10	73
Balance	(1,068)	(1,257)	(1,068)	(1,257)
Investments and Other
Before Tax
Balance	1	(14)	2	2
Changes in value	0	17	(1)	1
Amounts reclassified to earnings	0	0	0	0
Balance	1	3	1	3
Accumulated Other Comprehensive Income (Loss)
Total
Balance	(1,126)	(771)	(1,139)	(718)
Balance	$ (1,114)	$ (1,259)	$ (1,114)	$ (1,259)

AOCI Attributable To Parent, Before Tax [Roll Forward]

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AOCI Attributable To Parent, Tax [Roll Forward]

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount before tax of increase (decrease) in accumulated equity from transactions and other events and circumstances from non-owner sources, attributable to parent. Excludes net income (loss), and accumulated changes in equity from transactions resulting from investments by owners (distributions to owners).

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Amount of tax expense (benefit) allocated to accumulated other comprehensive income (loss) attributable to parent.

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Amount before tax and reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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

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

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

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

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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