|**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 31,201620152014Numerator:Net income—basic and diluted$591$634$525Denominator:Basic weighted-average common shares outstanding164.5164.0163.5Effect of share-based awards:Stock options1.11.01.0Nonvested shares0.90.60.6Diluted weighted-average shares166.5165.6165.1Earnings per share:Basic$3.59$3.87$3.21Diluted3.553.833.18Number of anti-dilutive share-based awards0.30.40.7
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|(In millions except per share data)                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|                                                      | 2016                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Numerator:                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Net income—basic and diluted                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Denominator:                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Basic weighted-average common shares outstanding      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Effect of share-based awards:                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Stock options                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Nonvested shares                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Diluted weighted-average shares                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Earnings per share:                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Basic                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Diluted                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Number of anti-dilutive share-based awards            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
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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.
+ ReferencesReference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257
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