Pension and Other Postemployment Benefits (Details 4) - Pension - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Reconciliation of changes in the fair value of pension investments
Beginning balance	$ 6,714
Actual return on plan assets:
Ending balance	6,916	$ 6,714
Real Estate Funds
Reconciliation of changes in the fair value of pension investments
Beginning balance	631
Actual return on plan assets:
Ending balance	665	631
Level 3 \| Real Estate Funds
Reconciliation of changes in the fair value of pension investments
Beginning balance	631	615
Actual return on plan assets:
Unrealized gains	102	3
Realized gains (losses)	(65)	10
Transfers in (out)	(3)	3
Ending balance	$ 665	$ 631

Defined Benefit Plan Actual Return On Plan Assets Realized Gains Losses.

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- Definition

Defined Benefit Plan Actual Return On Plan Assets Unrealized Gains Losses.

+ References

No definition available.

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- Definition

Defined Benefit Plan, Fair Value Of Plan Assets, Excluding Net Receivables (Payables), Taxes and Accrued Income

+ References

No definition available.

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- Definition

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

+ References

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan, for assets transferred into (out of) Level 3 of fair value hierarchy. Includes, but is not limited to, transfer due to change in observability of significant inputs.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(02)(C)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921

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