Supplemental Other Comprehensive Income (Loss) Information - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Equity [Abstract]
Unrecognized pension and other retiree benefit costs, aftertax	$ 1,038	$ 923
Foreign currency translation adjustments	$ 3,155	$ 2,927

Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains or losses.

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