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Share Based Compensation - Option Grant Information (Details) - Options [Member] - Stock Options [Member]
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 1.80% 1.60% 1.10%
Dividend yield 5.20% 5.20% 5.40%
Historical volatility factor 24.00% 23.60% 35.60%
Weighted-average expected life 7 years 6 years 6 years