v3.20.4
Summary of Significant Accounting Policies - Narrative (Details)
$ in Millions
 3 Months Ended 12 Months Ended
Jul. 01, 2020
USD ($)
Apr. 01, 2020
USD ($)
shares
Dec. 31, 2020
USD ($)
Sep. 30, 2020
USD ($)
Jun. 30, 2020
USD ($)
Mar. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Sep. 30, 2019
USD ($)
Jun. 30, 2019
USD ($)
Mar. 31, 2019
USD ($)
Dec. 31, 2020
USD ($)
unit
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Jan. 01, 2020
USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                            
Device upgrade period                     18 months      
Number of reporting units | unit                     2      
Fixed period                     15 years      
Federal Universal Service Fund and other fees                     $ 267 $ 93 $ 161  
Revenues     $ 20,341 $ 19,272 $ 17,671 $ 11,113 $ 11,878 $ 11,061 $ 10,979 $ 11,080 $ 68,397 44,998 43,310  
Average amortization period, deferred contract costs (in months)     24 months               24 months      
Advertising expense                     $ 1,800 1,600 1,700  
Accumulated deficit     $ 5,836       $ 8,833       $ 5,836 8,833    
Roaming and other service revenues | Reclassification                            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                            
Revenues                       $ 506 $ 449  
Minimum                            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                            
Lessee leasing arrangements, operating leases, term of contract (years)     5 years               5 years      
Option to extend lease term                     5 years      
Lessee leasing arrangements, finance leases, term of contract     2 years               2 years      
Minimum | EIP Securitization Arrangement                            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                            
Equipment installment plan, maximum payment term                     24 months      
Maximum                            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                            
Lessee leasing arrangements, operating leases, term of contract (years)     15 years               15 years      
Option to extend lease term                     35 years      
Lessee leasing arrangements, finance leases, term of contract     5 years               5 years      
Accounting Standards Update 2016-13                            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                            
Allowance for credit losses                           $ (91)
Deferred tax assets                           24
Accumulated deficit                           $ 67
Prepaid Business | T-Mobile and Sprint | DISH                            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                            
Payments for asset acquisition $ 1,400                          
Sprint                            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                            
Exchange ratio (in shares) | shares   0.10256                        
Exchange ratio (in shares) | shares   9.75                        
Total term of agreement                     30 years      
Deferred tax assets   $ 848                        
Sprint | Minimum                            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                            
Agreements with educational and certain non-profit institutions, term                     5 years      
Sprint | Maximum                            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                            
Agreements with educational and certain non-profit institutions, term                     10 years