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Compensation and Benefit Plans (Black-Scholes Option Pricing Model Assumptions) (Details) - Stock options
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected terms (in years) 5 years 8 months 12 days 5 years 10 months 24 days 5 years 10 months 24 days
Risk-free interest rate, minimum 2.10% 1.20% 1.60%
Risk-free interest rate, maximum 2.30% 2.20% 2.10%
Weighted-average expected dividend yield 2.70% 2.90% 2.60%
Expected volatility, minimum 17.80% 17.20% 16.40%
Expected volatility, maximum 20.90% 17.50% 17.00%
Weighted-average volatility 17.90% 17.40% 16.50%
Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected dividend yield 2.70% 2.50% 2.60%
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected dividend yield 3.80% 3.00% 3.20%