v3.8.0.1
Earnings Per Share (Antidilutive Securities Excluded From the Computation of Diluted Earnings Per Share) (Details) - $ / shares
shares in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]      
Weighted average shares of antidilutive security excluded from computation of diluted earnings per share (in shares) 0.4 2.7 2.4
Stock Options | Treasury Stock Method      
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]      
Weighted average shares of antidilutive security excluded from computation of diluted earnings per share (in shares) 0.3 2.7 2.4
Weighted average exercise price of options excluded from computation of diluted earnings per share (in dollars per share) $ 110.18 $ 83.97 $ 87.97
Stock Options | Direct Equity Adjustment      
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]      
Weighted average shares of antidilutive security excluded from computation of diluted earnings per share (in shares) 0.0 0.0 0.0
Antidilutive shares based on application of the treasury stock method [Member]      
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]      
Weighted average shares of antidilutive security excluded from computation of diluted earnings per share (in shares) 0.1 0.0 0.0
Employee And Non Employee Restricted Stock Shares Restricted Stock Units Performance Shares And Performance Units | Direct Equity Adjustment      
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]      
Weighted average shares of antidilutive security excluded from computation of diluted earnings per share (in shares) 0.0 0.0 0.0