v3.25.1
Taxation - Additional information (Details) - EUR (€)
€ in Millions
 12 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Mar. 31, 2023
Taxation      
Unused Tax Losses Available for Carryforward € 134,596 € 136,588  
Unremitted earnings of subsidiaries for which no deferred tax liability has been recognised 39,199 38,380  
Losses for which no deferred tax is recognised 56,483 56,344  
Tax losses utilized during the period € 433    
Percentage of deferred tax assets 2.80%    
Deferred tax assets € 19,033 20,177 € 19,316
LUXEMBOURG      
Taxation      
Unused Tax Losses Available for Carryforward € 65,200 67,016  
Corporate tax rate (as a percent) 1.00%    
Cash flow projection period to determine recoverable tax losses 5 years    
Utilisation period after reporting date beyond which deferred tax assets are not recognised 60 years    
LUXEMBOURG | Not later than 10 years      
Taxation      
Percentage of deferred tax expected to be used 20.00%    
Deferred tax assets € 3,065 3,306  
LUXEMBOURG | Not later than 20 years      
Taxation      
Percentage of deferred tax expected to be used 40.00%    
Deferred tax assets € 6,194 6,344  
LUXEMBOURG | Cable & Wireless Worldwide Group company      
Taxation      
Losses for which no deferred tax is recognised 9,136 9,136  
LUXEMBOURG | Tax losses on tax deductible impairments following Luxembourg tax reform      
Taxation      
Increase in deferred tax assets 719    
Taxe losses in current year 1,815    
Deferred tax assets 0    
Additional tax losses disposal of investments € 15,958 15,933  
Tax loss carryforward expiration period 17 years    
LUXEMBOURG | Tax losses      
Taxation      
Deferred tax assets € 15,563 16,714  
GERMANY      
Taxation      
Utilisation period of tax losses (in years) 5 years    
Deferred tax assets € 1,950 2,029  
UK      
Taxation      
Deferred tax assets € 2,566 2,485  
Cash flow projection period to determine recoverable tax losses 5 years    
UK | Tax losses that can only be offset against future capital gains      
Taxation      
Tax losses arising from subsidiaries for offset against future capital gains € 29,762 € 29,713  
Deferred tax assets € 0    
Minimum | LUXEMBOURG      
Taxation      
Corporate tax rate (as a percent) 1.00%    
Period over which tax losses are expected to be fully utilised 47 years 52 years  
Percentage of reasonably possible increase or decrease in forecast income 5.00%    
Increase or decrease in tax loss utilisation period based on reasonably possible increase or decrease in forecast income 3 years    
Minimum | LUXEMBOURG | Internal financing, centralised procurement, and international roaming activities      
Taxation      
Annual taxable profit consistently generated € 1    
Minimum | GERMANY      
Taxation      
Period over which trading tax losses are expected to be fully utilised 4 years    
Period over which corporate tax losses are expected to be fully utilised 14 years    
Minimum | UK      
Taxation      
Percentage of reasonably possible increase or decrease in forecast income 5.00%    
Maximum | LUXEMBOURG      
Taxation      
Expiration period of group's tax losses 15 years    
Period over which tax losses are expected to be fully utilised 52 years 57 years  
Percentage of reasonably possible increase or decrease in forecast income (10.00%)    
Increase or decrease in tax loss utilisation period based on reasonably possible increase or decrease in forecast income 6 years    
Maximum | GERMANY      
Taxation      
Period over which trading tax losses are expected to be fully utilised 5 years    
Period over which corporate tax losses are expected to be fully utilised 15 years    
Maximum | UK      
Taxation      
Percentage of reasonably possible increase or decrease in forecast income 10.00%