Marketable and Other Securities Fair Value of Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Marketable Securities [Line Items]
Total cash and cash equivalents	$ 15,087	$ 15,512
Cash and cash equivalents	205	219
Total restricted cash	2,684	2,336
Due in one year or less	4,741
Due between one and five years	4,683
Total available-for-sale debt securities with contractual maturities	9,424
Cash and Cash Equivalents [Member]
Marketable Securities [Line Items]
Cash and time deposits	7,248	6,962
Total available-for-sale debt securities with contractual maturities	3,166	5,736
Cash and Cash Equivalents [Member] \| Level 1 [Member]
Marketable Securities [Line Items]
Money market funds	4,673	2,814
Marketable Debt Securities [Member]
Marketable Securities [Line Items]
Total available-for-sale debt securities with contractual maturities	6,924	8,313
Restricted cash - cash equivalents [Member] \| Level 1 [Member]
Marketable Securities [Line Items]
Money market funds	2,479	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	1,307	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	2,028	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	1,222	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	3,414	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	666	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	637	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	$ 816	$ 703

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

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Fair value of available-for-sale debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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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.

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Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, 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.

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