Stock-Based Compensation - Compensation expense (Details) - USD ($) $ in Millions  | 
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2023  | 
Jun. 30, 2022  | 
Jun. 30, 2023  | 
Jun. 30, 2022  | 
|
| Stock-Based Compensation | ||||
| Stock-based compensation | $ 8 | $ 9 | $ 16 | $ 18 | 
| X | ||||||||||
- Definition Amount of expense for award under share-based payment arrangement. Excludes amount capitalized. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
  | 
| X | ||||||||||
- References No definition available. 
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