v3.19.2
financial instruments - Accounts receivable (Details) - Customer accounts receivable - CAD ($)
$ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Jun. 30, 2019
Dec. 31, 2018
Mar. 31, 2017
Dec. 31, 2016
Credit risk                  
Weighted average age of receivables     27 days   30 days        
Weighted average age of past-due receivables     60 days   56 days        
Receivable account balances $ 1,243   $ 1,210   $ 1,210 $ 1,243 $ 1,210    
Written off amounts charged to allowance for doubtful accounts still subject to enforcement           403 353    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     (1,210)            
Balance, end of period (1,243)   (1,243)   (1,210)        
Less than 30 days past billing date                  
Credit risk                  
Receivable account balances 922   749   749 922 749    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     (749)            
Balance, end of period (922)   (922)   (749)        
30-60 days past billing date                  
Credit risk                  
Receivable account balances 216   344   344 216 344    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     (344)            
Balance, end of period (216)   (216)   (344)        
61-90 days past billing date                  
Credit risk                  
Receivable account balances 53   72   72 53 72    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     (72)            
Balance, end of period (53)   (53)   (72)        
More than 90 days past billing date                  
Credit risk                  
Receivable account balances 52   45   45 52 45    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     (45)            
Balance, end of period (52)   (52)   (45)        
Cost/Gross amount                  
Credit risk                  
Receivable account balances 1,285   1,263   1,263 1,285 1,263    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     (1,263)            
Balance, end of period (1,285)   (1,285)   (1,263)        
Cost/Gross amount | Less than 30 days past billing date                  
Credit risk                  
Receivable account balances 934   762   762 934 762    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     (762)            
Balance, end of period (934)   (934)   (762)        
Cost/Gross amount | 30-60 days past billing date                  
Credit risk                  
Receivable account balances 224   354   354 224 354    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     (354)            
Balance, end of period (224)   (224)   (354)        
Cost/Gross amount | 61-90 days past billing date                  
Credit risk                  
Receivable account balances 59   80   80 59 80    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     (80)            
Balance, end of period (59)   (59)   (80)        
Cost/Gross amount | More than 90 days past billing date                  
Credit risk                  
Receivable account balances 68   67   67 68 67    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     (67)            
Balance, end of period (68)   (68)   (67)        
Allowance for doubtful accounts                  
Credit risk                  
Receivable account balances (42) $ (43) (53) $ (53) (53) (42) (53) $ (47) $ (43)
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period   43 53 53 53        
Additions (doubtful accounts expense) 10 11 21 27          
Accounts written off, net of recoveries (11) (13) (33) (27)          
Other   1 1 3          
Balance, end of period 42 $ 46 42 $ 46 53        
Allowance for doubtful accounts | Less than 30 days past billing date                  
Credit risk                  
Receivable account balances (12)   (13)   (13) (12) (13)    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     13            
Balance, end of period 12   12   13        
Allowance for doubtful accounts | 30-60 days past billing date                  
Credit risk                  
Receivable account balances (8)   (10)   (10) (8) (10)    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     10            
Balance, end of period 8   8   10        
Allowance for doubtful accounts | 61-90 days past billing date                  
Credit risk                  
Receivable account balances (6)   (8)   (8) (6) (8)    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     8            
Balance, end of period 6   6   8        
Allowance for doubtful accounts | More than 90 days past billing date                  
Credit risk                  
Receivable account balances (16)   (22)   (22) $ (16) $ (22)    
Summary of activity related to allowance for doubtful accounts                  
Balance, beginning of period     22            
Balance, end of period $ 16   $ 16   $ 22