Pension and Other Postemployment Benefits (Details 4) - Pension - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Reconciliation of changes in the fair value of pension investments
Beginning balance	$ 6,198
Actual return on plan assets:
Ending balance	6,714	$ 6,198
Real Estate Funds
Reconciliation of changes in the fair value of pension investments
Beginning balance	615
Actual return on plan assets:
Ending balance	631	615
Level 3 \| Real Estate Funds
Reconciliation of changes in the fair value of pension investments
Beginning balance	615	587
Actual return on plan assets:
Unrealized gains	3	29
Realized gains (losses)	10	14
Transfers in (out)	3	(15)
Ending balance	$ 631	$ 615

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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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, 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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-SubTopic 10
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