Pension and Other Postretirement Benefit Plans (Obligations and Funded Status at End of Year) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Postretirement Benefits
Funded status
Fair value of plan assets	$ 0	$ 0	$ 0
Benefit obligations	394	376	441
Funded status	(394)	(376)
Amounts recognized in the consolidated balance sheet
Noncurrent asset	0	0
Current liability	(42)	(42)
Noncurrent liability	(352)	(334)
Amount recognized	(394)	(376)
Amounts recognized in accumulated other comprehensive loss (pre-tax)
Net actuarial loss	17	3
Prior service (credit) cost	(20)	(40)
Amount recognized	(3)	(37)
United States Pension Benefits \| Pension Benefits
Funded status
Fair value of plan assets	2,746	2,664	2,741
Benefit obligations	3,415	3,415	3,470
Funded status	(669)	(751)
Amounts recognized in the consolidated balance sheet
Noncurrent asset	0	0
Current liability	(16)	(14)
Noncurrent liability	(653)	(737)
Amount recognized	(669)	(751)
Amounts recognized in accumulated other comprehensive loss (pre-tax)
Net actuarial loss	1,380	1,426
Prior service (credit) cost	(4)	(7)
Amount recognized	1,376	1,419
Foreign Pension Benefits \| Pension Benefits
Funded status
Fair value of plan assets	571	510	552
Benefit obligations	952	855	$ 865
Funded status	(381)	(345)
Amounts recognized in the consolidated balance sheet
Noncurrent asset	11	2
Current liability	(16)	(10)
Noncurrent liability	(376)	(337)
Amount recognized	(381)	(345)
Amounts recognized in accumulated other comprehensive loss (pre-tax)
Net actuarial loss	201	176
Prior service (credit) cost	(4)	(3)
Amount recognized	$ 197	$ 173

Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount of asset (liability), recognized in statement of financial position, for defined benefit pension and other postretirement plans.

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Amount of asset, recognized in statement of financial position, for overfunded defined benefit pension and other postretirement plans.

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Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

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Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

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Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as current.

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Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as noncurrent.

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