Pension and Other Postretirement Benefit Plans (Obligations and Funded Status at End of Year) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Postretirement Benefits
Funded status
Fair value of plan assets	$ 0	$ 0	$ 0
Benefit obligations	356	394	376
Funded status	(356)	(394)
Amounts recognized in the consolidated balance sheets
Noncurrent asset	0	0
Current liability	(38)	(42)
Noncurrent liability	(318)	(352)
Amount recognized	(356)	(394)
Amounts recognized in accumulated other comprehensive loss (pre-tax)
Net actuarial loss	1	17
Prior service (credit) cost	(16)	(20)
Amount recognized	(15)	(3)
United States Pension Benefits \| Pension Benefits
Funded status
Fair value of plan assets	2,676	2,746	2,664
Benefit obligations	3,033	3,415	3,415
Funded status	(357)	(669)
Amounts recognized in the consolidated balance sheets
Noncurrent asset	0	0
Current liability	(38)	(16)
Noncurrent liability	(319)	(653)
Amount recognized	(357)	(669)
Amounts recognized in accumulated other comprehensive loss (pre-tax)
Net actuarial loss	1,445	1,380
Prior service (credit) cost	(1)	(4)
Amount recognized	1,444	1,376
Foreign Pension Benefits \| Pension Benefits
Funded status
Fair value of plan assets	518	571	510
Benefit obligations	834	952	$ 855
Funded status	(316)	(381)
Amounts recognized in the consolidated balance sheets
Noncurrent asset	12	11
Current liability	(10)	(16)
Noncurrent liability	(318)	(376)
Amount recognized	(316)	(381)
Amounts recognized in accumulated other comprehensive loss (pre-tax)
Net actuarial loss	192	201
Prior service (credit) cost	(2)	(4)
Amount recognized	$ 190	$ 197

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

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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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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