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Stock-Based Compensation (Narrative) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized 8,000,000      
Maximum shares available for grants 5,800,000.0      
Performance Share Units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Performance period 3 years      
Percentage of shares issued per share unit, minimum 0.00%      
Percentage of shares issued per share unit, maximum 200.00%      
Amounts paid to settle share units $ 83 $ 27 $ 33  
Compensation cost not yet recognized $ 25      
Expected weighted average recognition period for share-based compensation expense, in months 22 months      
Fair value of each share unit, per share $ 44.13 [1] $ 52.88 $ 38.90  
Closing common share price   $ 43.23 $ 46.13 $ 36.16
Three-year risk-free rate 1.31% 1.10% 0.78%  
Volatility rate, minimum 15.00% 12.00% 12.00%  
Volatility rate, maximum 20.00% 18.00% 18.00%  
[1] Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in 2016 under the 2014 Incentive Plan.