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Property And Equipment (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Property, Plant and Equipment [Line Items]      
Depreciation expense $ 176 $ 147 $ 124
Amortization expense on computer software and leasehold improvements 462 528 528
Computer software amortization 412 450 $ 465
Capitalized costs related to the internal development of software 4,783 $ 3,939  
Impairment of property and equipment $ 198