Cash, Cash Equivalents, and Marketable Securities - Fair Values on Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Total Estimated Fair Value
Cash equivalents and marketable securities	$ 16,779
Cost or Amortized Cost
Cash equivalents and marketable securities	16,789
Recurring
Schedule of Investments [Line Items]
Cash	8,658	$ 6,883
Total Estimated Fair Value
Cash, cash equivalents and short-term investments	25,504	26,581
Less: Restricted cash, cash equivalents, and marketable securities	(1,194)	(600)
Total cash, cash equivalents, and marketable securities	24,310	25,981
Cost or Amortized Cost
Cash, cash equivalents and short-term investments	25,481
Gross Unrealized Gains
Short-term investments	37
Gross Unrealized Losses
Short-term investments	(14)
Recurring \| Level 1 securities
Total Estimated Fair Value
Equity securities	67	51
Cost or Amortized Cost
Equity securities	34
Gross Unrealized Gains
Equity securities	33
Gross Unrealized Losses
Equity securities	0
Recurring \| Level 1 securities \| Money market funds
Schedule of Investments [Line Items]
Money market funds	4,625	11,940
Recurring \| Level 2 securities \| Foreign government and agency securities
Total Estimated Fair Value
Cash equivalents and marketable securities	807	337
Cost or Amortized Cost
Cash equivalents and marketable securities	807
Gross Unrealized Gains
Cash equivalents and marketable securities	0
Gross Unrealized Losses
Cash equivalents and marketable securities	0
Recurring \| Level 2 securities \| U.S. government and agency securities
Total Estimated Fair Value
Cash equivalents and marketable securities	5,393	4,816
Cost or Amortized Cost
Cash equivalents and marketable securities	5,400
Gross Unrealized Gains
Cash equivalents and marketable securities	2
Gross Unrealized Losses
Cash equivalents and marketable securities	(9)
Recurring \| Level 2 securities \| Corporate debt securities
Total Estimated Fair Value
Cash equivalents and marketable securities	4,402	2,104
Cost or Amortized Cost
Cash equivalents and marketable securities	4,403
Gross Unrealized Gains
Cash equivalents and marketable securities	2
Gross Unrealized Losses
Cash equivalents and marketable securities	(3)
Recurring \| Level 2 securities \| Asset-backed securities
Total Estimated Fair Value
Cash equivalents and marketable securities	851	353
Cost or Amortized Cost
Cash equivalents and marketable securities	853
Gross Unrealized Gains
Cash equivalents and marketable securities	0
Gross Unrealized Losses
Cash equivalents and marketable securities	(2)
Recurring \| Level 2 securities \| Other fixed income securities
Total Estimated Fair Value
Cash equivalents and marketable securities	701	$ 97
Cost or Amortized Cost
Cash equivalents and marketable securities	701
Gross Unrealized Gains
Cash equivalents and marketable securities	0
Gross Unrealized Losses
Cash equivalents and marketable securities	$ 0

Cash, Cash Equivalents And Available-For-Sale Securities, Amortized Cost Basis [Abstract]

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Cash, Cash Equivalents, And Short-Term Investments, Amortized Cost Basis

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Cash, Cash Equivalents, And Short-Term Investments, Current And Noncurrent

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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

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Amount 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Cash and investments whose use in whole or in part is restricted for the long-term, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

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