v3.26.1
financial instruments - Fair Values Derivatives (Details)
$ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2026
CAD ($)
$ / $
₱ / $
$ / €
TWh
$ / MWh
Dec. 31, 2025
CAD ($)
$ / €
$ / $
₱ / $
TWh
$ / MWh
financial instruments    
Current Assets, Fair value and carrying value $ 142 $ 8
Current Liabilities, Fair value and carrying value $ 21 $ 30
Derivative assets | Cash flow hedges    
financial instruments    
Hedge ratio 1.00% 1.00%
Derivative assets | Currency risk related to long-term debt | Cash flow hedges | U.S. Dollars    
financial instruments    
Spread included in fair value of derivative instruments $ (24) $ (22)
Current derivative assets    
financial instruments    
Current Assets, Fair value and carrying value 142 $ 8
Current derivative assets | Currency risk related to transactions against Pesos | HFT | U.S. Dollars    
financial instruments    
Maximum maturity date   2026
Current Assets, Notional amount $ 26 $ 30
Rate | ₱ / $ 66 59
Current derivative assets | Currency risk related to transactions against CAD | Cash flow hedges | U.S. Dollars    
financial instruments    
Maximum maturity date 2027 2026
Current Assets, Notional amount $ 528 $ 134
Current Assets, Fair value and carrying value $ 18 $ 1
Rate | $ / $ 1.36 1.35
Current derivative assets | Currency risk related to transactions against CAD | HFT | U.S. Dollars    
financial instruments    
Rate | $ / $ 1.36  
Current derivative assets | Currency risk related to transactions against USD | HFT | European euro    
financial instruments    
Maximum maturity date 2028 2028
Current Assets, Notional amount $ 48 $ 33
Current Assets, Fair value and carrying value $ 10 $ 6
Rate | $ / € 1.09 1.09
Current derivative assets | Currency risk related to long-term debt | Cash flow hedges | U.S. Dollars    
financial instruments    
Maximum maturity date 2027 2026
Current Assets, Notional amount $ 3,184 $ 1,170
Current Assets, Fair value and carrying value $ 114 $ 1
Rate | $ / $   1.37
Other long-term assets | Currency risk related to long-term debt | Cash flow hedges | U.S. Dollars    
financial instruments    
Maximum maturity date 2055 2055
Rate | $ / $ 1.31 1.32
Other Long-Term Assets, Notional amount $ 6,550 $ 4,219
Other Long-Term Assets, Fair value and carrying value 87 40
Current derivative liabilities    
financial instruments    
Current Liabilities, Fair value and carrying value $ 21 $ 30
Current derivative liabilities | Currency risk related to transactions against Pesos | HFT | U.S. Dollars    
financial instruments    
Maximum maturity date 2027 2026
Rate | ₱ / $ 59 58
Current Liabilities, Notional amount $ 257 $ 254
Current Liabilities, Fair value and carrying value $ 11 $ 6
Current derivative liabilities | Currency risk related to transactions against CAD | Cash flow hedges | U.S. Dollars    
financial instruments    
Maximum maturity date — 2026
Rate | $ / $   1.39
Current Liabilities, Notional amount   $ 374
Current Liabilities, Fair value and carrying value   $ 7
Current derivative liabilities | Currency risk related to long-term debt | Cash flow hedges | U.S. Dollars    
financial instruments    
Maximum maturity date 2026 2026
Rate | $ / $ 1.42 1.39
Current Liabilities, Notional amount $ 923 $ 733
Current Liabilities, Fair value and carrying value   $ 10
Current derivative liabilities | Other price risk associated with purchase of electrical power | Cash flow hedges    
financial instruments    
Maximum maturity date 2047 2047
Current Liabilities, Fair value and carrying value $ 10 $ 7
Electrical consumption commodity derivative, Notional amount (in TWh) | TWh 0.3 0.3
Electrical consumption commodity derivative, Price (CAD/MWh). | $ / MWh 26.51 32.41
Other long-term liabilities    
financial instruments    
Other Long-Term Liabilities, Fair value and carrying value $ 112 $ 167
Other long-term liabilities | Currency risk related to transactions against USD | HFT | European euro    
financial instruments    
Maximum maturity date 2028 2028
Rate | $ / € 1.09 1.09
Other Long-Term Liabilities, Notional amount $ 533 $ 568
Other Long-Term Liabilities, Fair value and carrying value $ 30 $ 44
Other long-term liabilities | Currency risk related to long-term debt | Cash flow hedges | U.S. Dollars    
financial instruments    
Maximum maturity date 2056 2056
Rate | $ / $ 1.35 1.33
Other Long-Term Liabilities, Notional amount $ 3,990 $ 7,332
Other Long-Term Liabilities, Fair value and carrying value $ 46 $ 102
Other long-term liabilities | Other price risk associated with purchase of electrical power | Cash flow hedges    
financial instruments    
Maximum maturity date 2047 2047
Other Long-Term Liabilities, Fair value and carrying value $ 36 $ 21
Electrical consumption commodity derivative, Notional amount (in TWh) | TWh 4.7 4.9
Electrical consumption commodity derivative, Price (CAD/MWh). | $ / MWh 41.63 40.92