RETIREMENT-RELATED BENEFITS - Contributions, Defined Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Pension Plans, Including Multi-employer Plans \| Non-U.S.
Pension Contributions
Estimated cash contributions to the defined benefit plans in next fiscal year	$ 400
Pension Plans \| Non-U.S.
Pension Contributions
Contributions by employer to defined benefit plans	368	$ 464
Contributions by employer - Cash	192	169
Contributions by employer - Noncash	176	295
Multi-employer Plans
Pension Contributions
Cash contribution by employer to non-U.S. multi-employer plans	40	43
Nonpension Postretirement Plans
Pension Contributions
Contributions by employer to defined benefit plans	394	305
Contributions by employer - Cash		80
Contributions by employer - Noncash	394	225
Excess cash transferred to the Active Employee Medical Trust	70
Nonpension Postretirement Plans \| U.S.
Pension Contributions
Contributions by employer to defined benefit plans	394	305
Nonpension Postretirement Plans \| Non-U.S.
Pension Contributions
Contributions by employer to defined benefit plans	$ 0	$ 0

Cash contributions made by the employer during the period to a defined benefit plan.

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- Definition

Noncash contributions made by the employer during the period to a defined benefit plan. These contributions may be in the form of securities.

+ References

No definition available.

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- Definition

Amount of increase (decrease) in plan assets of defined benefit plan from assets transferred into (from) plan.

+ References

No definition available.

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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
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- Definition

Amount of contributions expected to be received by defined benefit plan from employer in next fiscal year following latest fiscal year.

+ References

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- Definition

Amount of contributions made to multiemployer plan by employer.

+ References

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