|**Net Income Per Common Share (Tables)**              | 3 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)Three months ended March 31,20142013Numerator:Net income—basic and diluted$91$154Denominator:Basic weighted-average common shares outstanding163.4163.1Effect of stock-based awards:Stock options1.01.0Nonvested shares0.60.8Adjusted diluted weighted-average shares165.0164.9Earnings per share:Basic$0.56$0.95Diluted0.550.94Number of anti-dilutive stock-based awards0.72.1
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|(In millions except per share data)                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|                                                      | 2014                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Numerator:                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Net income—basic and diluted                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Denominator:                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Basic weighted-average common shares outstanding      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Effect of stock-based awards:                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Stock options                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Nonvested shares                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Adjusted diluted weighted-average shares              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Earnings per share:                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Basic                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Diluted                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Number of anti-dilutive stock-based awards            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
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