Marketable and Other Securities Fair Value of Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Marketable Securities [Line Items]
Total cash and cash equivalents	$ 18,435	$ 15,512
Total restricted cash	2,423	2,336
Due in one year or less	6,777
Due between one and five years	4,376
Total available-for-sale debt securities with contractual maturities	11,153
GM Cruise [Member]
Marketable Securities [Line Items]
Money market funds	1,800
Cash and Cash Equivalents [Member]
Marketable Securities [Line Items]
Cash and time deposits	7,144	6,962
Total available-for-sale debt securities with contractual maturities	5,922	5,736
Cash and Cash Equivalents [Member] \| Level 1 [Member]
Marketable Securities [Line Items]
Money market funds	5,369	2,814
Marketable Debt Securities [Member]
Marketable Securities [Line Items]
Total available-for-sale debt securities with contractual maturities	5,916	8,313
Restricted cash - cash equivalents [Member]
Marketable Securities [Line Items]
Cash and cash equivalents	198	219
Restricted cash - cash equivalents [Member] \| Level 1 [Member]
Marketable Securities [Line Items]
Money market funds	2,225	2,117
U.S. government and agencies [Member] \| Cash and Cash Equivalents [Member] \| Level 2 [Member]
Marketable Securities [Line Items]
Total available-for-sale debt securities with contractual maturities	1,115	750
U.S. government and agencies [Member] \| Marketable Debt Securities [Member] \| Level 2 [Member]
Marketable Securities [Line Items]
Total available-for-sale debt securities with contractual maturities	1,229	3,310
Corporate debt [Member] \| Cash and Cash Equivalents [Member] \| Level 2 [Member]
Marketable Securities [Line Items]
Total available-for-sale debt securities with contractual maturities	2,774	3,032
Corporate debt [Member] \| Marketable Debt Securities [Member] \| Level 2 [Member]
Marketable Securities [Line Items]
Total available-for-sale debt securities with contractual maturities	3,416	3,665
Mortgage and asset-backed [Member] \| Marketable Debt Securities [Member] \| Level 2 [Member]
Marketable Securities [Line Items]
Total available-for-sale debt securities with contractual maturities	685	635
Sovereign debt [Member] \| Cash and Cash Equivalents [Member] \| Level 2 [Member]
Marketable Securities [Line Items]
Total available-for-sale debt securities with contractual maturities	2,033	1,954
Sovereign debt [Member] \| Marketable Debt Securities [Member] \| Level 2 [Member]
Marketable Securities [Line Items]
Total available-for-sale debt securities with contractual maturities	$ 586	$ 703

Sum of cash (other than available-for-sale and trading securities) and time deposits.

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