Pension and Other Postemployment Benefits (Details 4) - Pension - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Reconciliation of changes in the fair value of pension investments
Beginning balance	$ 5,345
Actual return on plan assets:
Ending balance	6,198	$ 5,345
Private Equity Funds
Reconciliation of changes in the fair value of pension investments
Beginning balance	24
Actual return on plan assets:
Ending balance	33	24
Real Estate Funds
Reconciliation of changes in the fair value of pension investments
Beginning balance	587
Actual return on plan assets:
Ending balance	615	587
Level 3
Reconciliation of changes in the fair value of pension investments
Beginning balance	611
Actual return on plan assets:
Ending balance	648	611
Level 3 \| Private Equity Funds
Reconciliation of changes in the fair value of pension investments
Beginning balance	24	25
Actual return on plan assets:
Unrealized gains	1	0
Realized gains (losses)	1	(1)
Transfers in (out)	7	0
Ending balance	33	24
Level 3 \| Real Estate Funds
Reconciliation of changes in the fair value of pension investments
Beginning balance	587	421
Actual return on plan assets:
Unrealized gains	29	42
Realized gains (losses)	14	16
Transfers in (out)	(15)	108
Ending balance	$ 615	$ 587

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.

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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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Transfers in and out of Level 3. For example, transfers due to changes in the observability of significant inputs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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.

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