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Leases - RoU Narrative (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Jan. 01, 2019
Dec. 31, 2018
Disclosure of quantitative information about right-of-use assets [line items]        
Right of use Assets $ 4,119 $ 4,011   $ 4,372
Lease Liabilities $ 4,405 $ 4,339    
IFRS 16 Adjustments [member]        
Disclosure of quantitative information about right-of-use assets [line items]        
Right of use Assets     $ 4,000