Unsecured senior notes - General (Details)
¥ in Millions, $ in Millions
 1 Months Ended
Jun. 30, 2023
USD ($)
Nov. 30, 2021
USD ($)
Nov. 30, 2019
USD ($)
Nov. 30, 2017
USD ($)
Mar. 31, 2023
USD ($)
Mar. 31, 2023
CNY (¥)
Mar. 31, 2022
USD ($)
Mar. 31, 2022
CNY (¥)
Feb. 28, 2021
USD ($)
Dec. 31, 2017
USD ($)
Nov. 30, 2014
USD ($)
Unsecured senior notes                      
Unsecured senior notes                      
Carrying value | ¥           ¥ 101,865   ¥ 94,259      
Unamortized discount and debt issuance costs | ¥           665   668      
Total principal amounts of unsecured senior notes | ¥           102,530   94,927      
Less: current portion of principal amounts of unsecured senior notes | ¥           (4,801)          
Non-current portion of principal amounts of unsecured senior notes | ¥           ¥ 97,729   ¥ 94,927      
2014 Senior Notes                      
Unsecured senior notes                      
Principal amount | $                     $ 8,000
Repayment amount | $   $ 1,500 $ 2,250 $ 1,300              
2017 Senior Notes                      
Unsecured senior notes                      
Principal amount | $                   $ 7,000  
Repayment amount | $ $ 700                    
2021 Senior Notes                      
Unsecured senior notes                      
Principal amount | $                 $ 5,000    
US$700 million 2.800% notes due 2023 | Unsecured senior notes                      
Unsecured senior notes                      
Principal amount | $         $ 700   $ 700        
Fixed interest rate         2.80% 2.80% 2.80% 2.80%      
Carrying value | ¥           ¥ 4,800   ¥ 4,439      
Effective interest rate         2.90% 2.90% 2.90% 2.90%      
US$2,250 million 3.600% notes due 2024 | Unsecured senior notes                      
Unsecured senior notes                      
Principal amount | $         $ 2,250   $ 2,250        
Fixed interest rate         3.60% 3.60% 3.60% 3.60%      
Carrying value | ¥           ¥ 15,410   ¥ 14,256      
Effective interest rate         3.68% 3.68% 3.68% 3.68%      
US$2,550 million 3.400% notes due 2027 | Unsecured senior notes                      
Unsecured senior notes                      
Principal amount | $         $ 2,550   $ 2,550        
Fixed interest rate         3.40% 3.40% 3.40% 3.40%      
Carrying value | ¥           ¥ 17,397   ¥ 16,091      
Effective interest rate         3.52% 3.52% 3.52% 3.52%      
US$1,500 million 2.125% notes due 2031 | Unsecured senior notes                      
Unsecured senior notes                      
Principal amount | $         $ 1,500   $ 1,500        
Fixed interest rate         2.125% 2.125% 2.125% 2.125%      
Carrying value | ¥           ¥ 10,234   ¥ 9,469      
Effective interest rate         2.20% 2.20% 2.20% 2.20%      
US$700 million 4.500% notes due 2034 | Unsecured senior notes                      
Unsecured senior notes                      
Principal amount | $         $ 700   $ 700        
Fixed interest rate         4.50% 4.50% 4.50% 4.50%      
Carrying value | ¥           ¥ 4,754   ¥ 4,400      
Effective interest rate         4.60% 4.60% 4.60% 4.60%      
US$1,000 million 4.000% notes due 2037 | Unsecured senior notes                      
Unsecured senior notes                      
Principal amount | $         $ 1,000   $ 1,000        
Fixed interest rate         4.00% 4.00% 4.00% 4.00%      
Carrying value | ¥           ¥ 6,807   ¥ 6,300      
Effective interest rate         4.06% 4.06% 4.06% 4.06%      
US$1,000 million 2.700% notes due 2041 | Unsecured senior notes                      
Unsecured senior notes                      
Principal amount | $         $ 1,000   $ 1,000        
Fixed interest rate         2.70% 2.70% 2.70% 2.70%      
Carrying value | ¥           ¥ 6,761   ¥ 6,256      
Effective interest rate         2.80% 2.80% 2.80% 2.80%      
US$1,750 million 4.200% notes due 2047 | Unsecured senior notes                      
Unsecured senior notes                      
Principal amount | $         $ 1,750   $ 1,750        
Fixed interest rate         4.20% 4.20% 4.20% 4.20%      
Carrying value | ¥           ¥ 11,898   ¥ 11,014      
Effective interest rate         4.25% 4.25% 4.25% 4.25%      
US$1,500 million 3.150% notes due 2051 | Unsecured senior notes                      
Unsecured senior notes                      
Principal amount | $         $ 1,500   $ 1,500        
Fixed interest rate         3.15% 3.15% 3.15% 3.15%      
Carrying value | ¥           ¥ 10,206   ¥ 9,448      
Effective interest rate         3.19% 3.19% 3.19% 3.19%      
US$1,000 million 4.400% notes due 2057 | Unsecured senior notes                      
Unsecured senior notes                      
Principal amount | $         $ 1,000   $ 1,000        
Fixed interest rate         4.40% 4.40% 4.40% 4.40%      
Carrying value | ¥           ¥ 6,795   ¥ 6,290      
Effective interest rate         4.44% 4.44% 4.44% 4.44%      
US$1,000 million 3.250% notes due 2061 | Unsecured senior notes                      
Unsecured senior notes                      
Principal amount | $         $ 1,000   $ 1,000        
Fixed interest rate         3.25% 3.25% 3.25% 3.25%      
Carrying value | ¥           ¥ 6,803   ¥ 6,296      
Effective interest rate         3.28% 3.28% 3.28% 3.28%