|**Net Income Per Common Share (Tables)**              | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|----------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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|**Earnings Per Share [Abstract]**                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Calculations For Basic And Diluted Earnings Per Share | The table shows calculations for basic and diluted earnings per share:(In millions, except per share data)Years ended December 31,202220212020Numerator:Net income (loss)—basic and diluted$(486)$2,946$1,216Denominator:Basic weighted-average common shares outstanding158.8161.0161.2Effect of share-based awards:Stock options—1.10.7Nonvested shares—0.60.5Diluted weighted-average shares158.8162.7162.4Earnings (loss) per share:Basic$(3.06)$18.29$7.55Diluted(3.06)18.107.49Number of anti-dilutive share-based awards2.20.81.4
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|(In millions, except per share data)                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|                                                      | 2022                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Numerator:                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Net income (loss)—basic and diluted                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Denominator:                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Basic weighted-average common shares outstanding      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Effect of share-based awards:                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Stock options                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Nonvested shares                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Diluted weighted-average shares                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Earnings (loss) per share:                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Basic                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Diluted                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|Number of anti-dilutive share-based awards            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
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X- ReferencesNo definition available.
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duration X- DefinitionTabular disclosure of an entity's basic and diluted earnings per share calculations, including a reconciliation of numerators and denominators of the basic and diluted per-share computations for income from continuing operations.
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