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Earnings Per Common Share, Potentially Dilutive Securities (Details) (Stock Options [Member])
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Stock Options [Member]
     
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Amount of potentially dilutive securities excluded from computation of earnings per common share 4 6 14