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Equity (Share Repurchase Program) (Details) - USD ($)
 1 Months Ended 10 Months Ended 12 Months Ended
Jan. 31, 2017
Mar. 31, 2014
Jun. 30, 2014
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Jul. 31, 2014
Jul. 31, 2013
Equity, Class of Treasury Stock [Line Items]                
Number of shares called by warrants   25,800,000.0            
Exercise price of warrants (dollars per share)   $ 32.085            
Proceeds from issuance of warrants   $ 68,900,000   $ 0 $ 0 $ 68,900,000    
Purchase of treasury shares         $ 20,818,000 $ 126,889,000    
Expected future share repurchase amount       $ 300,000,000        
2013 Stock Repurchase Program                
Equity, Class of Treasury Stock [Line Items]                
Amount authorized to repurchase shares               $ 100,000,000
Purchase of treasury shares (in shares)     4,400,000          
Purchase of treasury shares     $ 100,400,000          
2014 Stock Repurchase Program                
Equity, Class of Treasury Stock [Line Items]                
Amount authorized to repurchase shares             $ 100,000,000  
Purchase of treasury shares (in shares)         800,000.0 2,100,000.0    
Purchase of treasury shares         $ 20,800,000 $ 49,100,000    
Warrant class 1                
Equity, Class of Treasury Stock [Line Items]                
Number of shares called by warrants           15,200,000.0    
Threshold trading days expiration           50 days    
Warrant class 2                
Equity, Class of Treasury Stock [Line Items]                
Number of shares called by warrants           10,600,000.0    
Threshold trading days expiration           50 days    
Subsequent event                
Equity, Class of Treasury Stock [Line Items]                
Exercise price of warrants (dollars per share) $ 32.056              
Subsequent event | Synthetic Share Repurchase                
Equity, Class of Treasury Stock [Line Items]                
Stock repurchased $ 244,000,000              
Decrease of outstanding shares, rate 3.70%              
Common shares outstanding (in shares) 230,800,000              
Treasury shares (in shares) 4,950,000