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Stock-Based Compensation (Schedule Of Assumptions To Value SOSAR Awards Granted) (Details) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Risk-free interest rate 1.60% 1.00% 1.10%
Expected life 3 years 8 months 12 days 3 years 6 months 3 years 4 months 24 days
Expected dividend yield 0.00% 0.00% 0.00%
Volatility 29.90% 32.20% 30.80%
Performance Shares [Member]      
Risk-free interest rate 1.50% 0.90% 1.00%
Expected life 3 years 3 years 2 years 10 months 9 days
Expected dividend yield 0.00% 0.00% 0.00%
Volatility 29.90% 31.40% 33.70%
SOSARS [Member]      
Weighted-average grant date fair value $ 105.97 $ 117.48 $ 156.32