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Share and Unit-Based Plans: Stock Options Narrative (Details) - $ / shares
 12 Months Ended
Dec. 08, 2015
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 09, 2015
Share and unit-based plans            
Distributions paid, per share (in dollars per share) $ 2.00 $ 4.63 $ 2.51 $ 2.36    
Stock options            
Share and unit-based plans            
Grant date of award (in dollars per share)         $ 9.67  
Volatility rate (as a percent)         25.85%  
Dividend yield (as a percent)         3.69%  
Risk free rate (as a percent)         1.20%  
Current value (in dollars per share)         $ 59.57  
Expected term (in years)         8 years  
Stock options, outstanding, number (shares) 10,068 10,314 10,068 10,068 12,768 10,314
Stock options, outstanding, weighted average exercise price (in dollars per share) $ 59.57 $ 58.15 $ 59.57 $ 59.57 $ 54.69 $ 58.15