v3.25.2
Liquidity - additional information (Details)
€ in Millions, £ in Millions, $ in Billions
 1 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2025
USD ($)
Case
Mar. 31, 2025
USD ($)
tranche
Mar. 31, 2025
EUR (€)
tranche
Jan. 31, 2025
USD ($)
Jun. 30, 2025
GBP (£)
Jun. 30, 2024
GBP (£)
Dec. 31, 2024
USD ($)
Mar. 31, 2025
GBP (£)
Jan. 31, 2025
GBP (£)
Dec. 31, 2024
GBP (£)
Disclosure Of Financial Instruments [Line Items]                    
Ratio of floating rate borrowings after impact of derivatives         0.26 0.16 0.22     0.22
Ratio of fixed rate borrowings after impact of derivatives         0.74 0.84 0.78     0.78
Ratio of floating rate borrowings, excluding cash and other liquid assets in Canada         0.20 0.05 0.13     0.13
Ratio of fixed rate borrowings, excluding cash and other liquid assets in Canada         0.80 0.95 0.87     0.87
Liquidity risk                    
Disclosure Of Financial Instruments [Line Items]                    
Target average centrally managed bond maturity         5 years          
Average centrally managed debt maturity of bonds         10 years 9 years 2 months 12 days 9 years 6 months      
Peak maturity of centrally managed debt maturing in a rolling 12-month period         15.30% 15.60% 14.80%     14.80%
Borrowing capacity under US commercial paper programme | $             $ 4.0      
Borrowing capacity under Euro commercial paper programme         £ 3,000          
Commercial paper outstanding         700 £ 0       £ 0
Borrowings capacity         5,200          
Proceeds from issue of bonds, notes and debentures | $   $ 2.5              
Repayments of bonds $ 3.0   € 650              
Tranches | tranche   3 3              
Number of bonds repaid | Case 2                  
Liquidity risk | 364-day tranches                    
Disclosure Of Financial Instruments [Line Items]                    
Extension period   1 year 1 year              
Revolving credit facility               £ 2,500    
Period of tranche   364 days 364 days              
Liquidity risk | 5-year tranche                    
Disclosure Of Financial Instruments [Line Items]                    
Period of tranche   5 years 5 years              
Liquidity risk | 5-year tranche | Not later than one year                    
Disclosure Of Financial Instruments [Line Items]                    
Revolving credit facility               2,700    
Liquidity risk | 5-year tranche | Later than one year and not later than two years                    
Disclosure Of Financial Instruments [Line Items]                    
Revolving credit facility               £ 2,500    
Liquidity risk | Bilateral facilities                    
Disclosure Of Financial Instruments [Line Items]                    
Short term borrowing capacity         1,350          
Bilateral facility withdrawn and outstanding         100          
Undrawn borrowing facilities         £ 2,600          
Liquidity risk | Term loan facility                    
Disclosure Of Financial Instruments [Line Items]                    
Borrowings capacity                 £ 460  
Liquidity risk | Fixed rate                    
Disclosure Of Financial Instruments [Line Items]                    
Target for floating to fixed rate debt         50.00%          
Liquidity risk | Top of range                    
Disclosure Of Financial Instruments [Line Items]                    
Target centrally managed debt maturing in a rolling 12-month period         20.00%