| **Net Income Per Common Share**   | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
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| **Earnings Per Share [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
| Net Income Per Common Share       | Basic earnings per share are computed based on the weighted average number of common shares outstanding. Diluted earnings per share are computed based on the weighted average number of common and dilutive potential common shares outstanding using the treasury stock method. The table shows calculations for basic and diluted earnings per share:(In millions except per share data) Three months ended September 30, Nine months ended September 30, 2015 2014 2015 2014Numerator:        Net income—basic and diluted $174 $183 $478 $358Denominator:        Basic weighted-average common shares  outstanding 164.0 163.5 164.1 163.5Effect of share-based awards:        Stock options 1.0 0.9 0.9 0.9Nonvested shares 0.5 0.6 0.5 0.6Diluted weighted-average shares  165.5 165.0 165.5 165.0Earnings per share:        Basic $1.06 $1.12 $2.91 $2.19Diluted 1.05 1.11 2.89 2.17Number of anti-dilutive share-based awards: 0.3 0.7 0.7 0.7         The sources of dilution of our common shares are certain equity-based awards. See our 2014 Annual Report on Form 10-K, Item 8, Note 17, Share-Based Associate Compensation Plans, Page 154, for information about equity-based awards. The above table shows the number of anti-dilutive share-based awards for the three and nine months endedSeptember 30, 2015 and 2014. We did not include these share-based awards in the computation of net income per common share (diluted) because their exercise would have anti-dilutive effects. |

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| - Definition
The entire disclosure for earnings per share.
+ References
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