Retirement-Related Benefits - Nonpension Postretirement Contributions (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Nonpension Postretirement Plans \| U.S.
Retirement-Related Benefits
Contributions by employer - Noncash	$ 292	$ 215

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.

No definition available.

Name:	us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration