v3.21.2
Receivables and Expected Credit Losses - Unamortized Imputed Discount and Allowance for Credit Losses (Details) - USD ($)
$ in Millions
 6 Months Ended 12 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]      
Allowance for credit losses and imputed discount, beginning of period $ 799 $ 460 $ 460
Bad debt expense 154 346  
Write-offs, net of recoveries (251) (152)  
Change in imputed discount on short-term and long-term EIP receivables 91 10  
Impact on the imputed discount from sales of EIP receivables (73) (81)  
Allowance for credit losses and imputed discount, end of period 720 674 799
Cumulative Effect, Period of Adoption, Adjustment      
Financing Receivable, Allowance for Credit Loss [Roll Forward]      
Allowance for credit losses and imputed discount, beginning of period 0 91 91
Allowance for credit losses and imputed discount, end of period     0
Accounts Receivable Allowance      
Financing Receivable, Allowance for Credit Loss [Roll Forward]      
Allowance for credit losses and imputed discount, beginning of period 194 61 61
Bad debt expense 76 178  
Write-offs, net of recoveries (147) (56)  
Allowance for credit losses and imputed discount, end of period 123 183 194
Accounts Receivable Allowance | Cumulative Effect, Period of Adoption, Adjustment      
Financing Receivable, Allowance for Credit Loss [Roll Forward]      
Allowance for credit losses and imputed discount, beginning of period $ 0 0 0
Allowance for credit losses and imputed discount, end of period     $ 0
EIP Receivables Allowance      
Financing Receivable, Allowance for Credit Loss [Line Items]      
Weighted average effective imputed interest rate (percentage) 6.30%   6.70%
Financing Receivable, Allowance for Credit Loss [Roll Forward]      
Allowance for credit losses and imputed discount, beginning of period $ 605 399 $ 399
Bad debt expense 78 168  
Write-offs, net of recoveries (104) (96)  
Change in imputed discount on short-term and long-term EIP receivables 91 10  
Impact on the imputed discount from sales of EIP receivables (73) (81)  
Allowance for credit losses and imputed discount, end of period 597 491 605
EIP Receivables Allowance | Cumulative Effect, Period of Adoption, Adjustment      
Financing Receivable, Allowance for Credit Loss [Roll Forward]      
Allowance for credit losses and imputed discount, beginning of period $ 0 $ 91 91
Allowance for credit losses and imputed discount, end of period     $ 0