Stock-Based Compensation - Cost (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based compensation cost, allocation of recognized costs
Pre-tax stock-based compensation cost	$ 510	$ 534	$ 544
Income tax benefits	(116)	(131)	(179)
Net stock-based compensation cost	393	403	364
Unrecognized compensation cost related to non-vested awards	$ 821	851
Unrecognized compensation cost related to non-vested awards, weighted average period of recognition	2 years 7 months 6 days
Cost
Stock-based compensation cost, allocation of recognized costs
Pre-tax stock-based compensation cost	$ 82	91	88
SG&A expense
Stock-based compensation cost, allocation of recognized costs
Pre-tax stock-based compensation cost	361	384	401
Research, development and engineering
Stock-based compensation cost, allocation of recognized costs
Pre-tax stock-based compensation cost	$ 67	$ 59	$ 55

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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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.

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Unrecognized cost of unvested share-based compensation awards.

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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