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           Activity in Deferred Compensation Program (Detail) (USD $) 
        In Millions, unless otherwise specified  | 
        9 Months Ended | |||||
|---|---|---|---|---|---|---|
| 
           Sep. 30, 2012 
         | 
        
           Dec. 31, 2011 
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           Sep. 30, 2012
 
          Treasury Stock [Member] 
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           Sep. 30, 2011
 
          Treasury Stock [Member] 
         | 
        
           Sep. 30, 2012
 
          Deferred Compensation Obligations 
         | 
        
           Sep. 30, 2011
 
          Deferred Compensation Obligations 
         | 
      |
| Stockholders Equity Note [Roll Forward] | ||||||
| Balance at beginning of period | (2) | (2) | (2) | (2) | ||
| Reinvested dividends | 0 | 0 | ||||
| Benefit payments | 0 | 0 | ||||
| Balance at end of period | (2) | (2) | (2) | (2) | ||
| Balance at beginning of period | $ 7,529 | $ 7,035 | $ (88) | $ (103) | $ 88 | $ 103 | 
| Reinvested dividends | (3) | (3) | 3 | 3 | ||
| Benefit payments | 14 | 19 | (14) | (19) | ||
| Balance at end of period | $ 7,529 | $ 7,035 | $ (77) | $ (87) | $ 77 | $ 87 | 
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- Definition 
          Deferred Compensation Payment No definition available. 
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- Definition 
          The number of shares issued pursuant to the terms of the deferred compensation plan as of the balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Details 
          
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- Definition 
          Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Number of shares issued during the period from a dividend reinvestment plan (DRIP). A dividend reinvestment plan allows the shareholders to reinvest dividends paid to them by the entity on new issues of stock by the entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Value of stock issued during the period from a dividend reinvestment plan (DRIP). A dividend reinvestment plan allows the holder of the stock to reinvest dividends paid to them by the entity on new issues of stock by the entity. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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