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Financial Instruments - Information on Available-for-sale Investments (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 | Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items] |  |
Debt securities, fair value | $ 14,206 | $ 14,908
Publicly traded equity securities, fair value | 332 |
Available-for-sale Securities, Equity Securities |  | 275
Total debt and publicly traded equity securities, fair value | 14,538 |
Available-for-sale Securities |  | 15,183
Debt securities, amortized cost | 14,374 | 14,976
Publicly traded equity securities, amortized cost |  | 265
Total debt and publicly traded equity securities, amortized cost |  | 15,241
Debt securities, unrealized gains | 4 | 11
Equity securities, unrealized gains |  | 16
Total debt and publicly traded equity securities, unrealized gains |  | 27
Debt securities, unrealized losses | (172) | (79)
Equity securities, unrealized losses |  | (6)
Total debt and publicly traded equity securities, unrealized losses |  | (85)
Unrealized net gain | 44 |
Commercial paper |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Debt securities, fair value | 130 | 159
Debt securities, amortized cost | 130 | 159
Debt securities, unrealized gains | 0 | 0
Debt securities, unrealized losses | 0 | 0
Corporate notes and bonds |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Debt securities, fair value | 9,860 | 9,806
Debt securities, amortized cost | 9,978 | 9,837
Debt securities, unrealized gains | 3 | 9
Debt securities, unrealized losses | (121) | (40)
U.S. government and agency securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Debt securities, fair value | 1,810 | 2,042
Debt securities, amortized cost | 1,833 | 2,059
Debt securities, unrealized gains | 0 | 0
Debt securities, unrealized losses | (23) | (17)
Asset-backed securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Debt securities, fair value | 1,569 | 1,542
Debt securities, amortized cost | 1,585 | 1,548
Debt securities, unrealized gains | 1 | 1
Debt securities, unrealized losses | (17) | (7)
Foreign government bonds |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Debt securities, fair value | 759 | 733
Debt securities, amortized cost | 769 | 739
Debt securities, unrealized gains | 0 | 0
Debt securities, unrealized losses | (10) | (6)
Mortgage-backed securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Debt securities, fair value | 78 | 626
Debt securities, amortized cost | 79 | 634
Debt securities, unrealized gains | 0 | 1
Debt securities, unrealized losses | $ (1) | $ (9)

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