|**Earnings Per Share (Tables)**                                                                                                            | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
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|**Earnings Per Share [Abstract]**                                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Calculation of Basic and Diluted Earnings (Loss) Per Share                                                                                 | The following table summarizes the calculation of basic and diluted earnings per share:Year Ended December 31,201220112010(millions, except per share amounts)Income from Continuing Operations Used for Diluted Earnings Per Share Calculation$965$412$631Weighted Average Number of Shares Outstanding, Basic178176175Incremental Shares From Assumed Conversion of Dilutive Stock Options and Restricted Stock232Weighted Average Number of Shares Outstanding, Diluted180179177Earnings from Continuing Operations Per Share, Basic$5.43$2.34$3.61Earnings from Continuing Operations Per Share, Diluted5.372.313.56Additional InformationNumber of antidilutive stock options, shares of restricted stock and shares of common stock in rabbi trust excluded from calculation above332Weighted average option exercise price per share$97.46$85.40$74.01
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|(millions, except per share amounts)                                                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Income from Continuing Operations Used for Diluted Earnings Per Share Calculation                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
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|Weighted Average Number of Shares Outstanding, Basic                                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Incremental Shares From Assumed Conversion of Dilutive Stock Options and Restricted Stock                                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Weighted Average Number of Shares Outstanding, Diluted                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Earnings from Continuing Operations Per Share, Basic                                                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Earnings from Continuing Operations Per Share, Diluted                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
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|Additional Information                                                                                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Number of antidilutive stock options, shares of restricted stock and shares of common stock in rabbi trust excluded from calculation above |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|Weighted average option exercise price per share                                                                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              

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