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Marketable Securities (Tables) | 12 Months Ended
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Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract] |
Summary of Marketable Securities [Table Text Block] |
| 2017 |  | 2016
| Cost |  | Unrealized Gains (Losses) |  | Fair Value |  | Cost |  | Unrealized Gains (Losses) |  | Fair Value
U.S. government securities | $ | 3 |  |  | $ | — |  |  | $ | 3 |  |  | $ | 2 |  |  | $ | — |  |  | $ | 2 |
Corporate securities | 5 |  |  |  |  |  | 5 |  |  | 2 |  |  |  |  |  | 2 |
Certificates of deposit | 27 |  |  |  |  |  | 27 |  |  | 22 |  |  |  |  | 22 |
Other | 4 |  |  | 1 |  |  | 5 |  |  | 4 |  |  |  |  |  | 4 |
Total marketable securities | $ | 39 |  |  | $ | 1 |  |  | $ | 40 |  |  | $ | 30 |  |  | $ | — |  |  | $ | 30 |

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- Definition Tabular disclosure of the reconciliation of available-for-sale securities from cost basis to fair value. + References No definition available. + Details
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