v3.19.3.a.u2
Preferred shares issued by a subsidiary company - (Details)
$ in Millions
 2 Months Ended 12 Months Ended
Dec. 31, 2019
$ / shares
shares
Feb. 27, 2020
USD ($)
shares
Dec. 31, 2019
USD ($)
shares
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2014
Dec. 31, 2009
$ / shares
shares
Dec. 31, 2007
$ / shares
shares
Preferred shares issued by a subsidiary company                
Preferred shares repurchased and retired | $     $ 8.0 $ 8.0 $ 3.1      
Net income attributable to preferred shares of a subsidiary company | $     1.2 (0.4) (5.6)      
Cumulative Preferred Stock                
Preferred shares issued by a subsidiary company                
Preferred shares repurchased and retired | $     $ 8.0 8.0 3.1      
Series 1 Shares                
Preferred shares issued by a subsidiary company                
Preferred shares repurchased and retired (in shares)     427,500          
Series 1 Shares | Subsequent event                
Preferred shares issued by a subsidiary company                
Preferred shares repurchased and retired (in shares)   247,894            
Preferred shares repurchased and retired | $   $ 3.1            
Series 2 Shares                
Preferred shares issued by a subsidiary company                
Preferred shares repurchased and retired (in shares)     100,377          
Series 3 Shares                
Preferred shares issued by a subsidiary company                
Preferred shares repurchased and retired (in shares)     148,311          
Subsidiary Issuer | Cumulative Preferred Stock                
Preferred shares issued by a subsidiary company                
Dividend paid | $     $ 7.4 8.3 8.7      
Net income attributable to preferred shares of a subsidiary company | $     $ 8.6 $ 7.9 $ 3.0      
Subsidiary Issuer | Series 1 Shares                
Preferred shares issued by a subsidiary company                
Number of shares issued in transaction               5,000,000
Dividend rate on preferred shares (as a percent)               4.85%
Issuance price per share | $ / shares               $ 25.00
Preferred Stock, Shares Outstanding 3,847,500              
Redemption price after specified date and thereafter (in Canadian dollars per share) | $ / shares               $ 25.00
Subsidiary Issuer | Series 2 Shares                
Preferred shares issued by a subsidiary company                
Number of shares issued in transaction             4,000,000  
Dividend rate on preferred shares (as a percent) 5.67%           7.00%  
Issuance price per share | $ / shares             $ 25.00  
Preferred Stock, Shares Outstanding 2,504,131              
Redemption price after specified date and thereafter (in Canadian dollars per share) | $ / shares $ 25.00              
Period for declaration of dividend at reset rate           5 years    
Reference rate for dividend           five-year Government of Canada bond yield    
Percentage points added to the reference rate           4.18%    
Shares Converted     23,618          
Subsidiary Issuer | Series 3 Shares                
Preferred shares issued by a subsidiary company                
Dividend rate on preferred shares (as a percent) 5.83%   5.83%          
Preferred Stock, Shares Outstanding 1,077,391              
Redemption price after specified date and thereafter (in Canadian dollars per share) | $ / shares $ 25.00              
Period for declaration of dividend at reset rate     5 years          
Reference rate for dividend     90-day Government of Canada Treasury bill rate          
Percentage points added to the reference rate 4.18%              
Shares Converted     295,032