Pension and Other Postretirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 14	$ 13	$ 28	$ 27
Interest cost	20	21	40	42
Expected return on plan assets	(20)	(34)	(39)	(69)
Amortization of unrecognized prior service credit	(24)	(26)	(49)	(53)
Termination benefits	0	0	1	1
Curtailments	(2)	(1)	(5)	(2)
Net periodic benefit cost	(12)	(27)	(24)	(54)
International \| Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	63	62	124	120
Interest cost	42	52	83	105
Expected return on plan assets	(97)	(97)	(191)	(193)
Amortization of unrecognized prior service credit	(3)	(3)	(5)	(6)
Net loss amortization	24	21	47	43
Termination benefits	1	0	2	0
Curtailments	(1)	0	(1)	1
Net periodic benefit cost	29	35	59	70
U.S. \| Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	77	73	154	146
Interest cost	113	113	226	226
Expected return on plan assets	(218)	(210)	(436)	(420)
Amortization of unrecognized prior service credit	(13)	(14)	(27)	(27)
Net loss amortization	44	29	89	57
Termination benefits	3	1	8	5
Curtailments	1	0	4	0
Net periodic benefit cost	$ 7	$ (8)	$ 18	$ (13)

Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.

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Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.

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Amount of cost of providing special or contractual termination benefits payable from defined benefit plan.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.

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Amount of cost recognized for passage of time related to defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(2)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Amount of net periodic benefit cost (credit) for defined benefit plan.

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Amount of gain (loss) recognized in net periodic benefit (cost) credit from event reducing expected years of future service of present employees or eliminating accrual of defined benefits for some or all future services of present employees.

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
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-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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