Postemployment benefit plans (Details 3) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
U.S. Pension Benefits
Change in plan assets:
Fair value of plan assets, beginning of year	$ 11,354	$ 11,440
Actual return on plan assets	1,692	860
Foreign currency exchange rates	0	0
Company contributions	1,350	36
Participant contributions	0	0
Benefits paid	(977)	(970)
Settlements and termination benefits	(3)	(12)
Fair value of plan assets, end of year	$ 13,416	11,354
Information about plan asset allocations
Rebalancing of plan assets outside of target allocation (as a percent)	5.00%
U.S. Pension Benefits \| Equities
Information about plan asset allocations
Target allocation of plan assets (as a percent)	30.00%
U.S. Pension Benefits \| Debt securities
Information about plan asset allocations
Target allocation of plan assets (as a percent)	70.00%
U.S. Pension Benefits \| Real estate
Change in plan assets:
Fair value of plan assets, beginning of year	$ 10
Fair value of plan assets, end of year	10	10
Non-U.S. Pension Benefits
Change in plan assets:
Fair value of plan assets, beginning of year	3,887	3,890
Actual return on plan assets	350	503
Foreign currency exchange rates	278	(392)
Company contributions	107	117
Participant contributions	6	7
Benefits paid	(203)	(238)
Settlements and termination benefits	(120)	0
Fair value of plan assets, end of year	$ 4,305	3,887
Non-U.S. Pension Benefits \| Equities
Information about plan asset allocations
Target allocation of plan assets (as a percent)	38.00%
Non-U.S. Pension Benefits \| Debt securities
Information about plan asset allocations
Target allocation of plan assets (as a percent)	54.00%
Non-U.S. Pension Benefits \| Real estate
Change in plan assets:
Fair value of plan assets, beginning of year	$ 179
Fair value of plan assets, end of year	$ 186	179
Information about plan asset allocations
Target allocation of plan assets (as a percent)	5.00%
Non-U.S. Pension Benefits \| Other
Information about plan asset allocations
Target allocation of plan assets (as a percent)	3.00%
Other Postretirement Benefits
Change in plan assets:
Fair value of plan assets, beginning of year	$ 550	650
Actual return on plan assets	101	55
Foreign currency exchange rates	0	0
Company contributions	155	176
Participant contributions	59	57
Benefits paid	(361)	(388)
Settlements and termination benefits	0	0
Fair value of plan assets, end of year	$ 504	$ 550
Other Postretirement Benefits \| Equities
Information about plan asset allocations
Target allocation of plan assets (as a percent)	70.00%
Other Postretirement Benefits \| Debt securities
Information about plan asset allocations
Target allocation of plan assets (as a percent)	30.00%

The amount of change in plan assets due to settlements and termination benefits.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

This element represents the range of rebalancing of plan assets outside of the target allocation.

+ References

No definition available.

+ Details

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- Definition

Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

+ References

+ Details

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Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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.

+ References

+ Details

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Balance Type:	debit
Period Type:	instant

- References

No definition available.

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- Definition

Amount of payment to participant under defined benefit plan which decreases plan assets. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 60
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(5)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	duration

- Definition

Amount of contributions received by defined benefit plan from participant which increases plan assets.

+ References

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- Definition

Amount of foreign currency translation gain (loss) which increases (decreases) plan assets of defined benefit plan.

+ References

+ Details

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- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

+ Details

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- Details

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- Details

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