Fair Value Measurements - Schedule of Reconciliation of Level 3 Investments Securities (Footnotes) (Details) - USD ($) $ in Millions |
Jun. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Estimated Fair Value | ||
| Securities with a loss shorter than 12 months | $ 105 | $ 26 |
| Securities with a loss shorter than 12 months | 3 | 1 |
| Unrealized Losses | ||
| Securities with a loss longer than 12 months | 44 | 46 |
| Securities with a loss longer than 12 months | $ 2 | $ 2 |
| X | ||||||||||
- Definition Debt Securities, Available-For-Sale, Continuous Unrealized Loss Position, 12 Months Or Longer No definition available.
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| X | ||||||||||
- Definition Debt Securities, Available-For-Sale, Continuous Unrealized Loss Position, 12 Months Or Longer, Accumulated Loss No definition available.
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| X | ||||||||||
- Definition Debt Securities, Available-For-Sale, Unrealized Loss Position No definition available.
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| X | ||||||||||
- Definition Debt Securities, Available-For-Sale, Unrealized Loss Position, Accumulated Loss No definition available.
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- References No definition available.
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