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Marketable and Other Securities Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2018 | Jun. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017
Marketable Securities [Line Items] |  |  |  |  |  |
Cash and cash equivalents | $ 18,435 |  |  | $ 18,435 |  | $ 15,512
Sale proceeds from investments classified as available-for-sale and sold prior to maturity | 1,700 |  | $ 3,700 | 3,600 | $ 5,100 |
GM Korea [Member] |  |  |  |  |  |
Marketable Securities [Line Items] |  |  |  |  |  |
Cash and cash equivalents | 364 |  |  | 364 |  |
Level 3 [Member] |  |  |  |  |  |
Marketable Securities [Line Items] |  |  |  |  |  |
Fair value of equity securities | $ 884 | $ 884 |  | $ 884 |  |
Level 3 [Member] | Interest Income and Other Non-Operating Income, Net [Member] |  |  |  |  |  |
Marketable Securities [Line Items] |  |  |  |  |  |
Unrealized gain on equity securities |  | $ 142 |  |  |  |

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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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- Definition Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740 + Details
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