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Shareholders' Equity Shareholders' Equity (Common Stock Issued With The Exercise Of Stock Options (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Stockholders' Equity Note [Abstract]      
Shares issued (in shares) 1.0 0.3 1.3
Proceeds from the exercise of stock options $ 39.7 $ 8.4 $ 30.0
Average exercise price per share (in dollars per share) $ 37.85 $ 31.21 $ 23.33