v3.20.4
Receivables and Expected Credit Losses - Unamortized Imputed Discount and Allowance for Credit Losses (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]      
Allowance for credit losses and imputed discount, beginning of period $ 460 $ 516 $ 482
Bad debt expense 602 307 297
Write-offs, net of recoveries (380) (332) (328)
Change in imputed discount on short-term and long-term EIP receivables 171 136 250
Impact on the imputed discount from sales of EIP receivables (145) (167) (185)
Allowance for credit losses and imputed discount, end of period 799 460 516
Cumulative Effect, Period of Adoption, Adjustment      
Financing Receivable, Allowance for Credit Loss [Roll Forward]      
Allowance for credit losses and imputed discount, beginning of period 91    
Allowance for credit losses and imputed discount, end of period   91  
Accounts Receivable Allowance      
Financing Receivable, Allowance for Credit Loss [Roll Forward]      
Allowance for credit losses and imputed discount, beginning of period 61 67 86
Bad debt expense 338 77 69
Write-offs, net of recoveries (205) (83) (88)
Allowance for credit losses and imputed discount, end of period 194 61 67
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    
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) 6.70% 8.80%  
Financing Receivable, Allowance for Credit Loss [Roll Forward]      
Allowance for credit losses and imputed discount, beginning of period $ 399 $ 449 396
Bad debt expense 264 230 228
Write-offs, net of recoveries (175) (249) (240)
Change in imputed discount on short-term and long-term EIP receivables 171 136 250
Impact on the imputed discount from sales of EIP receivables (145) (167) (185)
Allowance for credit losses and imputed discount, end of period 605 399 $ 449
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 $ 91    
Allowance for credit losses and imputed discount, end of period   $ 91