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Common Shareholders’ Equity (Details 3) - $ / shares
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 06, 2017
Apr. 12, 2017
Dec. 06, 2016
Apr. 13, 2016
Dec. 02, 2015
Apr. 15, 2015
Dec. 02, 2014
Interim dividend [Member]                      
Disclosure of Common Shareholders’ Equity [Line Items]                      
Dividend paid date Jan. 05, 2018 Jan. 06, 2017 Jan. 08, 2016 Jan. 09, 2015              
Dividend per Share $ 70.0000 $ 66.0000 $ 66.0000 $ 63.0000 $ 70   $ 66   $ 66   $ 63
Year of dividend 2017 2016 2015 2014              
Final dividend [Member]                      
Disclosure of Common Shareholders’ Equity [Line Items]                      
Dividend paid date   Apr. 26, 2017 Apr. 22, 2016 Apr. 23, 2015              
Dividend per Share   $ 110.32236 $ 97.47388 $ 98.78138   $ 110.32236   $ 97.47388   $ 98.78138  
Year of dividend   2016 2015 2014