Marketable and Other Securities Narrative (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | |||
|---|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
Dec. 31, 2017 |
|
| Marketable Securities [Line Items] | |||||
| Cash and cash equivalents | $ 15,087 | $ 15,087 | $ 15,512 | ||
| Sale proceeds from investments classified as available-for-sale and sold prior to maturity | 1,000 | $ 750 | 2,000 | $ 1,400 | |
| GM Cruise [Member] | |||||
| Marketable Securities [Line Items] | |||||
| Cash and cash equivalents | 2,000 | 2,000 | |||
| GM Korea [Member] | |||||
| Marketable Securities [Line Items] | |||||
| Cash and cash equivalents | 361 | 361 | |||
| Level 3 [Member] | |||||
| Marketable Securities [Line Items] | |||||
| Adjustment of equity security to fair value | 884 | 884 | |||
| Level 3 [Member] | Interest Income and Other Non-Operating Income, Net [Member] | |||||
| Marketable Securities [Line Items] | |||||
| Unrealized gain on equity securities | $ 142 | $ 142 | |||