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Financial Risk Management - Summary of Hedging instruments (Detail) - Interest rate risk [member]
$ in Millions
Jun. 30, 2021
USD ($)
Disclosure of detailed information about hedging instruments [line items]  
Notional value $ 16,810
Interest rate swap contract [member] | USD [member]  
Disclosure of detailed information about hedging instruments [line items]  
Notional value 11,950
cross currency interest rate swaps [member] | EUR [member]  
Disclosure of detailed information about hedging instruments [line items]  
Notional value 3,187
cross currency interest rate swaps [member] | GBP [member]  
Disclosure of detailed information about hedging instruments [line items]  
Notional value 1,673
Not​ later​ than​ two​ years​ [member]  
Disclosure of detailed information about hedging instruments [line items]  
Notional value 3,306
Not​ later​ than​ two​ years​ [member] | Interest rate swap contract [member] | USD [member]  
Disclosure of detailed information about hedging instruments [line items]  
Notional value 1,979
Not​ later​ than​ two​ years​ [member] | cross currency interest rate swaps [member] | EUR [member]  
Disclosure of detailed information about hedging instruments [line items]  
Notional value 404
Not​ later​ than​ two​ years​ [member] | cross currency interest rate swaps [member] | GBP [member]  
Disclosure of detailed information about hedging instruments [line items]  
Notional value $ 923