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Stockholders' Equity - Common Stock (Details) | 1 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 $ / shares shares | Dec. 31, 2018 vote $ / shares shares | Dec. 31, 2017 $ / shares shares | Dec. 31, 2016 shares
Class of Stock [Line Items] |  |  |  |
Common stock, par value (in dollars per share) | $ / shares | $ 0.00001 | $ 0.00001 | $ 0.00001 |
Restricted Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Shares granted (in shares) |  | 16,200,000 | 21,500,000 | 16,600,000
Co-Founder Grants | Restricted Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Shares granted (in shares) | 14,700,000 | 14,700,000 | 14,700,000 |
Class A common stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Votes per share | vote |  | 1 |  |
Common stock, shares authorized (in shares) | 533,300,000.0 | 2,400,000,000.0 | 533,300,000.0 |
Common stock, par value (in dollars per share) | $ / shares |  | $ 0.00001 |  |
Common stock, shares issued (in shares) | 8,900,000 | 211,000,000 | 8,900,000 |
Common stock, shares outstanding (in shares) | 8,900,000 | 211,000,000 | 8,900,000 |
Class B common stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Votes per share | vote |  | 10 |  |
Shares converted in conversion (in shares) |  | 157,000,000 |  |
Common stock, shares authorized (in shares) | 466,700,000.0 | 475,000,000.0 | 466,700,000.0 |
Common stock, par value (in dollars per share) | $ / shares |  | $ 0.00001 |  |
Common stock, shares issued (in shares) | 187,900,000 | 198,600,000 | 187,900,000 |
Common stock, shares outstanding (in shares) | 187,900,000 | 198,600,000 | 187,900,000 |
Class C common stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Votes per share | vote |  | 0 |  |
Common stock, shares authorized (in shares) | 0 | 800,000,000.0 | 0 |
Common stock, par value (in dollars per share) | $ / shares |  | $ 0.00001 |  |
Common stock, shares issued (in shares) | 0 | 0 | 0 |
Common stock, shares outstanding (in shares) | 0 | 0 | 0 |

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- Definition Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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