|**Earnings Per Share (Tables)**                                    | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
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|**Earnings Per Share [Abstract]**                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Schedule of Weighted Average Number of Shares                      | Our calculation of diluted earnings per common share assumes that any common shares outstanding were increased by shares that would be issued upon exercise of those stock units for which the average market price for the period exceeds the exercise price less the shares that could have been purchased by the Company with the related proceeds, including compensation expense measured but not yet recognized, net of tax.Three Months Ended September 30,Nine Months Ended September 30,(in millions)2014201320142013Weighted-average number of common shares outstanding — basic114.4113.6114.2113.5Stock-settled stock appreciation rights0.60.80.60.8Restricted stock units2.01.41.91.3Adjusted weighted-average shares and assumed conversions — diluted117.0115.8116.7115.6
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|                                                                   | Three Months Ended September 30,                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
|(in millions)                                                      | 2014                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted-average number of common shares outstanding — basic       | 114.4                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|Stock-settled stock appreciation rights                            | 0.6                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Restricted stock units                                             | 2.0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Adjusted weighted-average shares and assumed conversions — diluted | 117.0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    

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