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Capital Stock (Textuals) (Details) - USD ($)
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Aug. 24, 2015
Aug. 18, 2012
Equity, Class of Treasury Stock [Line Items]        
Shares repurchased (in shares - less than 0.1 million) 100,000 100,000    
Shares repurchased (less than $1 million) $ 8,000,000 $ 5,000,000    
Share Repurchase Programs        
Equity, Class of Treasury Stock [Line Items]        
Shares repurchased (in shares - less than 0.1 million) 400,000      
Shares repurchased (less than $1 million) $ 33,000,000      
2015 Stock Repurchase Program        
Equity, Class of Treasury Stock [Line Items]        
Stock repurchase program, authorized amount     $ 500,000,000  
Shares repurchased (in shares - less than 0.1 million) 300,000 0    
Shares repurchased (less than $1 million) $ 25,000,000 $ 0    
Remaining authorized amount of repurchase $ 388,000,000      
2012 Stock Repurchase Program        
Equity, Class of Treasury Stock [Line Items]        
Stock repurchase program, authorized amount       $ 2,000,000
Shares repurchased (in shares - less than 0.1 million) 0 0    
Shares repurchased (less than $1 million) $ 0 $ 0