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Investments (Tables) | 3 Months Ended
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Mar. 31, 2019
Investments, Debt and Equity Securities [Abstract] |
Amortized Cost, Gross Unrealized Gains and Losses, Fair Values of Investments | The amortized cost, gross unrealized gains, gross unrealized losses, and fair values of our investments as of March 31, 2019 and December 31, 2018 are presented below.
| March 31, 2019 | December 31, 2018
(in millions) | Amortized Cost | Gross Unrealized Gains | Gross Unrealized Losses | Fair Value | Amortized Cost | Gross Unrealized Gains | Gross Unrealized Losses | Fair Value
Asset-backed securities | $ | 35 |  | $ | — |  | $ | — |  | $ | 35 |  | $ | 33 |  | $ | — |  | $ | — |  | $ | 33 |
Corporate bonds | 100 |  | — |  | — |  | 100 |  | 99 |  | — |  | — |  | 99 |
U.S. government agencies and government- sponsored agencies | 6 |  | — |  | — |  | 6 |  | 7 |  | — |  | — |  | 7 |
U.S. treasuries | 47 |  | — |  | — |  | 47 |  | 46 |  | — |  | — |  | 46 |
Exchange traded fund | 1 |  | — |  | — |  | 1 |  | 1 |  | — |  | — |  | 1 |
Other debt securities | 6 |  | — |  | — |  | 6 |  | 9 |  | — |  | — |  | 9 |
Total | $ | 195 |  | $ | — |  | $ | — |  | $ | 195 |  | $ | 195 |  | $ | — |  | $ | — |  | $ | 195 |
Fair Value of Debt Investments by Contractual Maturity | The fair value of debt investments by contractual maturity are shown below:
(in millions) |  | March 31, 2019 |
One year or less |  | $ | 61 |  |
Over one year through five years |  | 117 |  |
Over five years through ten years |  | 7 |  |
Over ten years |  | 9 |  |
Total fair value |  | $ | 194 |  |
Proceeds from available-for-sale securities | The gross proceeds from sales and maturities of AFS securities for the three months ended March 31, 2019 and March 31, 2018 are presented below.
| Three Months Ended March 31,
(in millions) | 2019 | 2018
Gross proceeds from sales | $ | 14 |  | $ | — |
Gross proceeds from maturities | 17 |  | 14 |
Total | $ | 31 |  | $ | 14 |

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- Definition Debt Securities, Available-For-Sale, And Equity Securities, FV-NI [Table Text Block] + References No definition available. + Details
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- Definition Tabular disclosure 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/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -URI http://asc.fasb.org/topic&trid=2196928 + Details
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- Definition Tabular disclosure of maturities of an entity's investments as well as any other information pertinent to the investments. + References No definition available. + Details
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