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Financial Instruments - Information on Available-for-sale Investments (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018 | Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt securities, amortized cost | $ 4,076 |  | $ 4,076 |  | $ 7,340
Debt securities, unrealized gains | 50 |  | 50 |  | 6
Debt securities, unrealized losses | (3) |  | (3) |  | (85)
Debt securities, fair value | 4,123 |  | 4,123 |  | 7,261
Publicly traded equity securities, fair value | 756 |  | 756 |  | 456
Total debt and publicly traded equity securities, fair value | 4,879 |  | 4,879 |  | 7,717
Unrealized net gain | (39) | $ 7 | 75 | $ 50 |
Corporate notes and bonds |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt securities, amortized cost | 2,666 |  | 2,666 |  | 4,985
Debt securities, unrealized gains | 36 |  | 36 |  | 3
Debt securities, unrealized losses | (2) |  | (2) |  | (68)
Debt securities, fair value | 2,700 |  | 2,700 |  | 4,920
Asset-backed securities |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt securities, amortized cost | 789 |  | 789 |  | 1,285
Debt securities, unrealized gains | 4 |  | 4 |  | 1
Debt securities, unrealized losses | (1) |  | (1) |  | (11)
Debt securities, fair value | 792 |  | 792 |  | 1,275
U.S. government and agency securities |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt securities, amortized cost | 575 |  | 575 |  | 895
Debt securities, unrealized gains | 10 |  | 10 |  | 2
Debt securities, unrealized losses | 0 |  | 0 |  | (5)
Debt securities, fair value | 585 |  | 585 |  | 892
Foreign government bonds |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt securities, amortized cost | 41 |  | 41 |  | 167
Debt securities, unrealized gains | 0 |  | 0 |  | 0
Debt securities, unrealized losses | 0 |  | 0 |  | (1)
Debt securities, fair value | 41 |  | 41 |  | 166
Mortgage-backed securities |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt securities, amortized cost | 5 |  | 5 |  | 8
Debt securities, unrealized gains | 0 |  | 0 |  | 0
Debt securities, unrealized losses | 0 |  | 0 |  | 0
Debt securities, fair value | $ 5 |  | $ 5 |  | $ 8

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- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563 + Details
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- Definition Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563 + Details
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- Definition Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454 + Details
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563 + Details
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- Definition Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740 + Details
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