Employee Benefit Plans (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Employee Benefit Plans | |||
| Employer cash contribution | $ 9 | $ 9 | $ 7 |
| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Amount of cost for defined contribution plan. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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