v3.25.4
Financial and capital management - Market Risk Narrative (Details)
$ in Millions, $ in Millions
 12 Months Ended
Aug. 01, 2025
CAD ($)
Dec. 31, 2025
CAD ($)
Dec. 31, 2024
CAD ($)
Dec. 31, 2025
USD ($)
Sep. 23, 2025
CAD ($)
Sep. 23, 2025
USD ($)
Aug. 14, 2025
CAD ($)
Dec. 31, 2024
USD ($)
Disclosure of detailed information about hedged items [line items]                
Gains (losses) on change in fair value of derivatives   $ (9) $ (269)          
Loss on change in fair value of derivatives   $ 9 269          
Unsecured Term Loan                
Disclosure of detailed information about hedged items [line items]                
Maximum borrowing capacity         $ 692 $ 500    
Series M-65 Medium Term Note Debentures                
Disclosure of detailed information about hedged items [line items]                
Notional amount             $ 500  
Series M-66 Medium Term Note Debentures                
Disclosure of detailed information about hedged items [line items]                
Notional amount             600  
Series M-67 Medium Term Note Debentures                
Disclosure of detailed information about hedged items [line items]                
Notional amount             $ 500  
Currency risk                
Disclosure of detailed information about hedged items [line items]                
Percentage of possible change in risk variable   10.00%   10.00%        
Currency risk | Top of range                
Disclosure of detailed information about hedged items [line items]                
Reasonably possible change in risk variable impact on net earnings   $ (22)            
Sensitivity analysis for types of market risk, reasonably possible change in risk variable, impact on other comprehensive income   (146)            
Currency risk | Bottom of range                
Disclosure of detailed information about hedged items [line items]                
Reasonably possible change in risk variable impact on net earnings   15            
Sensitivity analysis for types of market risk, reasonably possible change in risk variable, impact on other comprehensive income   126            
Currency risk | Series US-9 Notes                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, liabilities   4            
Financial assets, at fair value     5          
Currency risk | Series US-10 Notes                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, liabilities   $ 17 44          
Interest rate risk                
Disclosure of detailed information about hedged items [line items]                
Percentage of possible change in risk variable   1.00%   1.00%        
Interest rate risk | Top of range                
Disclosure of detailed information about hedged items [line items]                
Sensitivity analysis for types of market risk, reasonably possible change in risk variable, impact on other comprehensive income   $ (3)            
Reasonably possible change in risk variable impact on net earnings   32            
Interest rate risk | Bottom of range                
Disclosure of detailed information about hedged items [line items]                
Sensitivity analysis for types of market risk, reasonably possible change in risk variable, impact on other comprehensive income   4            
Reasonably possible change in risk variable impact on net earnings   (26)            
Interest rate risk | Series A and Series B Notes Maturing in 2055                
Disclosure of detailed information about hedged items [line items]                
Notional amount   3            
Interest rate risk | Series M-55 Medium-term notes                
Disclosure of detailed information about hedged items [line items]                
Gains (losses) on change in fair value of derivatives   (3)            
Loss on change in fair value of derivatives   3            
Interest rate risk | Series M-55 Medium-term notes | Maturing in 2025                
Disclosure of detailed information about hedged items [line items]                
Notional amount   300            
Equity price risk                
Disclosure of detailed information about hedged items [line items]                
Gains (losses) on change in fair value of derivatives   $ (9) (269)          
Percentage of possible change in risk variable   5.00%   5.00%        
Reasonably possible change in risk variable impact on net earnings   $ (16)            
Loss on change in fair value of derivatives   9 269          
Forward contract | Equity price risk                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, liabilities   187 429          
Amortizing Cross Currency Interest Rate Swaps | Currency risk | Maturing in 2029                
Disclosure of detailed information about hedged items [line items]                
Notional amount   678   $ 487        
Hedging instrument, liabilities   11            
Interest rate swap contract | Series M-53 Medium Term Notes Debentures | Maturing in 2027                
Disclosure of detailed information about hedged items [line items]                
Notional amount     625          
Interest rate swap contract | Series M-52 Medium Term Notes Debentures | Maturing in 2030                
Disclosure of detailed information about hedged items [line items]                
Notional amount     250          
Interest rate swap contract | Series M-57 Medium Term Notes Debentures | Maturing in 2025 and 2032                
Disclosure of detailed information about hedged items [line items]                
Notional amount, swaps terminated     200          
Interest rate swap contract | Currency risk                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, assets   4            
Interest rate swap contract | Currency risk | Fair value hedges                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, liabilities   110            
Interest rate swap contract | Currency risk | Maturing in 2025 and 2026                
Disclosure of detailed information about hedged items [line items]                
Notional amount, financial instrument terminated   814   600        
Interest rate swap contract | Currency risk | Series US-2 Notes                
Disclosure of detailed information about hedged items [line items]                
Notional amount, financial instrument terminated   235   174        
Interest rate swap contract | Currency risk | Series US-4 Notes                
Disclosure of detailed information about hedged items [line items]                
Notional amount, financial instrument terminated   100   79        
Interest rate swap contract | Currency risk | Series US-5 Notes                
Disclosure of detailed information about hedged items [line items]                
Notional amount, financial instrument terminated   230   183        
Interest rate swap contract | Currency risk | Series US-6 Notes                
Disclosure of detailed information about hedged items [line items]                
Notional amount, financial instrument terminated   241   191        
Interest rate swap contract | Currency risk | Series US-7 Notes                
Disclosure of detailed information about hedged items [line items]                
Notional amount, financial instrument terminated   276   217        
Interest rate swap contract | Currency risk | Series A Notes                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, liabilities   69            
Initial net hedging liabilities   55            
Interest rate swap contract | Currency risk | Series A Notes | Maturing in 2030                
Disclosure of detailed information about hedged items [line items]                
Notional amount   1,468   1,000        
Interest rate swap contract | Currency risk | Series B Notes Maturing in 2055                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, liabilities   59            
Initial net hedging liabilities   55            
Interest rate swap contract | Currency risk | Series B Notes Maturing in 2055 | Maturing In 2035                
Disclosure of detailed information about hedged items [line items]                
Notional amount   1,288   878        
Interest rate swap contract | Currency risk | Series US-9 Notes | Fair value hedges                
Disclosure of detailed information about hedged items [line items]                
Notional amount     942         $ 700
Interest rate swap contract | Currency risk | Series US-10 Notes | Maturing in 2054                
Disclosure of detailed information about hedged items [line items]                
Notional amount     1,009         750
Interest rate swap contract | Interest rate risk | Maturing in 2028                
Disclosure of detailed information about hedged items [line items]                
Notional amount   200            
Hedging instrument, liabilities   9            
Interest rate swap contract | Interest rate risk | Series A Notes | Maturing in 2030                
Disclosure of detailed information about hedged items [line items]                
Notional amount   531   372        
Hedging instrument, assets terminated   9            
Interest rate swap contract | Interest rate risk | Series B Notes Maturing in 2055                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, assets   4            
Interest rate swap contract | Interest rate risk | Series B Notes Maturing in 2055 | Maturing In 2035                
Disclosure of detailed information about hedged items [line items]                
Notional amount   531   372        
Interest rate swap contract | Interest rate risk | Series M-45 Medium-term notes | Maturing in 2047                
Disclosure of detailed information about hedged items [line items]                
Notional amount   200            
Interest rate swap contract | Interest rate risk | Series M-65 Medium Term Note Debentures | Maturing in 2033                
Disclosure of detailed information about hedged items [line items]                
Notional amount   300            
Hedging instrument, liabilities   1            
Interest rate swap contract | Interest rate risk | Series M-66 Medium Term Note Debentures | Maturing in 2036                
Disclosure of detailed information about hedged items [line items]                
Notional amount   300            
Hedging instrument, liabilities   3            
Interest rate swap contract | Interest rate risk | Series M-62 Medium Term Notes Debentures                
Disclosure of detailed information about hedged items [line items]                
Notional amount, swaps terminated   105            
Interest rate swap contract | Interest rate risk | Series M-53 Medium Term Notes Debentures                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, assets     6          
Interest rate swap contract | Interest rate risk | Series M-52 Medium Term Notes Debentures                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, assets     6          
Interest rate swap contract | Interest rate risk | Series M-57 Medium Term Notes Debentures                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, assets terminated     6          
Foreign Exchange Swaps | Currency risk                
Disclosure of detailed information about hedged items [line items]                
Notional amount   521   372        
Hedging instrument, liabilities   13            
Initial net hedging liabilities   14            
Foreign Exchange Swaps | Currency risk | Maturing in 2025                
Disclosure of detailed information about hedged items [line items]                
Notional amount   524   372        
Hedging instrument, liabilities   2            
Hedging instrument, assets   13            
Foreign Exchange Swaps | Currency risk | Series A Notes                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, liabilities   12            
Initial net hedging liabilities   12            
Initial net hedging assets   9            
Foreign Exchange Swaps | Currency risk | Series A Notes | Maturing in 2025                
Disclosure of detailed information about hedged items [line items]                
Notional amount   1,398   1,000        
Foreign Exchange Swaps | Currency risk | Series B Notes Maturing in 2055                
Disclosure of detailed information about hedged items [line items]                
Initial net hedging liabilities   14            
Foreign Exchange Swaps | Currency risk | Series B Notes Maturing in 2055 | Maturing in 2025                
Disclosure of detailed information about hedged items [line items]                
Notional amount   1,769   1,250        
Foreign Exchange Swaps | Currency risk | Series B Notes                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, liabilities   24            
Notional amount, financial instrument terminated   643   456        
Foreign Exchange Swaps | Currency risk | Series B Notes | Maturing in 2025                
Disclosure of detailed information about hedged items [line items]                
Notional amount   1,167   828        
Currency Basis Rate Swap Contract | Currency risk                
Disclosure of detailed information about hedged items [line items]                
Notional amount     644          
Interest Rate Swaptions | Maturing in 2024                
Disclosure of detailed information about hedged items [line items]                
Notional amount     289         214
Interest Rate Swaptions | Series M-53 Medium Term Notes Debentures                
Disclosure of detailed information about hedged items [line items]                
Notional amount     625          
Hedging instrument, liabilities     6          
Interest Rate Swaptions | Series M-53 Medium Term Notes Debentures | Maturing in 2027                
Disclosure of detailed information about hedged items [line items]                
Notional amount     750          
Interest Rate Swaptions | Series M-17 Medium Term Notes Debentures | Maturing In 2035                
Disclosure of detailed information about hedged items [line items]                
Notional amount     300          
Interest Rate Swaptions | Interest rate risk | Maturing in 2030 and 2035                
Disclosure of detailed information about hedged items [line items]                
Notional amount   690            
Interest Rate Floor | Interest rate risk | Series M-62 Medium Term Notes Debentures | Maturing in 2029                
Disclosure of detailed information about hedged items [line items]                
Notional amount, financial instrument terminated   350            
Forward Starting Interest Rate Swap                
Disclosure of detailed information about hedged items [line items]                
Notional amount     1,080         800
Notional amount, swaps terminated     338         250
Notional amount, swaps unterminated     742         550
Forward Starting Interest Rate Swap | Maturing in 2030                
Disclosure of detailed information about hedged items [line items]                
Notional amount               400
Notional amount, swaps unterminated     275          
Forward Starting Interest Rate Swap | Maturing In 2035                
Disclosure of detailed information about hedged items [line items]                
Notional amount               $ 400
Notional amount, swaps unterminated     275          
Forward Starting Interest Rate Swap | Series US-10 Notes | Maturing in 2054                
Disclosure of detailed information about hedged items [line items]                
Notional amount     336          
Forward Starting Interest Rate Swap | Interest rate risk                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, liabilities   3            
Hedging instrument, assets   50 38          
Notional amount, swaps terminated   500   350        
Hedging instrument, assets terminated     7          
Forward Starting Interest Rate Swap | Interest rate risk | Maturing In 2055                
Disclosure of detailed information about hedged items [line items]                
Notional amount   423            
Forward Starting Interest Rate Swap | Interest rate risk | Series US-10 Notes                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, assets     20          
Forward Starting Interest Rate Swap | Interest rate risk | Series M-67 Medium Term Note Debentures                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, assets   25            
Interest Rate Options | Series M-62 Medium Term Notes Debentures | Maturing in 2029                
Disclosure of detailed information about hedged items [line items]                
Notional amount     440          
Interest Rate Options | Interest rate risk                
Disclosure of detailed information about hedged items [line items]                
Hedging instrument, assets terminated     $ 1          
Ziply Fiber                
Disclosure of detailed information about hedged items [line items]                
Gains (losses) on change in fair value of derivatives $ 7              
Loss on change in fair value of derivatives $ (7)              
Ziply Fiber | Currency risk                
Disclosure of detailed information about hedged items [line items]                
Cash deposits, hedging instrument   4,908   3,545        
Ziply Fiber | Currency risk | Unsecured Term Loan                
Disclosure of detailed information about hedged items [line items]                
Maximum borrowing capacity   697   500        
Ziply Fiber | Deal Contingent Foreign Exchange Forward Contracts | Currency risk                
Disclosure of detailed information about hedged items [line items]                
Notional amount   1,241   905        
Ziply Fiber | Forward contract | Currency risk                
Disclosure of detailed information about hedged items [line items]                
Notional amount   $ 1,402   $ 1,019