Share and Unit-Based Plans: SARs Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2014
SARs
Share and unit-based plans
Term of award (in years)	10 years
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	8 years
SARS granted prior to 2012
Share and unit-based plans
Grant date of award (in dollars per share)	$ 7.68
Volatility rate (as a percent)	22.52%
Dividend yield (as a percent)	5.23%
Risk free rate (as a percent)	3.15%
Current value (in dollars per share)	$ 61.17
Expected term	8 years