Retirement-Related Benefits - Contributions, Defined Benefit Pension Plans (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Pension Contributions
Contributions by employer - Noncash	$ 635	$ 598
Pension Plans, Including Multi-employer Plans \| Non-U.S.
Pension Contributions
Estimated cash contributions to the defined benefit plans in next fiscal year	$ 300

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Name:	us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant