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Fair Value Measurements - Schedule of Fair Value of Investment Assets (Details) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Carrying Value |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Amortized cost basis of investments | $ 92 | $ 95
Fair Value | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Investments fair value disclosure | 94 |
Fair Value | Level 2 | Certificates of Deposit and Commercial Paper |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Investments fair value disclosure | 0 |
Fair Value | Level 2 | Corporate Bonds |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Investments fair value disclosure | 58 |
Fair Value | Level 2 | Government Securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Investments fair value disclosure | 36 |
Fair Value | Level 2 | Auction Rate Securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Investments fair value disclosure | $ 0 |
Fair Value | Level 2 |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Investments fair value disclosure |  | 95
Fair Value | Level 2 | Certificates of Deposit and Commercial Paper |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Investments fair value disclosure |  | 0
Fair Value | Level 2 | Corporate Bonds |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Investments fair value disclosure |  | 61
Fair Value | Level 2 | Government Securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Investments fair value disclosure |  | 34
Fair Value | Level 2 | Auction Rate Securities |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Investments fair value disclosure |  | $ 0

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