v3.20.4
Additional Financial Information - Related Party Transactions (Details) - USD ($)
12 Months Ended
Apr. 01, 2020
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Oct. 28, 2020
Oct. 06, 2020
Jul. 04, 2020
Jun. 24, 2020
Apr. 09, 2020
Related Party Transaction [Line Items]                  
Principal Amount   $ 30,447,000,000              
Principal Issuances   54,750,000,000              
Senior Notes                  
Related Party Transaction [Line Items]                  
Principal Issuances         $ 4,750,000,000 $ 4,000,000,000.0   $ 4,000,000,000.0 $ 19,000,000,000.0
Sprint                  
Related Party Transaction [Line Items]                  
Principal Issuances   24,605,000,000              
DT | Sprint                  
Related Party Transaction [Line Items]                  
Payments for requisite consents to DT $ 13,000,000                
Affiliates                  
Related Party Transaction [Line Items]                  
Discount related to roaming expenses   (5,000,000) $ (9,000,000) $ 0          
Fees incurred for use of the T-Mobile brand   83,000,000 88,000,000 84,000,000          
International long distance agreement   47,000,000 39,000,000 36,000,000          
Reimbursement of certain administrative expenses   6,000,000 $ 11,000,000 $ 11,000,000          
Affiliates | DT | Sprint | Senior Notes                  
Related Party Transaction [Line Items]                  
Indebtedness to affiliates 4,000,000,000.0                
Secured Term Loan Facility | DT | Sprint                  
Related Party Transaction [Line Items]                  
Repayments of Debt 4,000,000,000.0                
Incremental term loan facility to affiliates due 2022 | Affiliates                  
Related Party Transaction [Line Items]                  
Principal Amount 2,000,000,000.0 2,000,000,000              
Incremental term loan facility to affiliates due 2024 | Affiliates                  
Related Party Transaction [Line Items]                  
Principal Amount 2,000,000,000.0 $ 2,000,000,000              
5.300% Senior Notes due 2021 | DT | Sprint | Senior Notes                  
Related Party Transaction [Line Items]                  
Principal Issuances $ 2,000,000,000.0                
Interest rate, stated percentage 5.30%                
5.300% Senior Notes due 2021 | Affiliates                  
Related Party Transaction [Line Items]                  
Interest rate, stated percentage   5.30%              
5.300% Senior Notes due 2021 | Affiliates | Senior Notes                  
Related Party Transaction [Line Items]                  
Interest rate, stated percentage   5.30%              
6.000% Senior Notes due 2024 | DT | Sprint | Senior Notes                  
Related Party Transaction [Line Items]                  
Principal Issuances $ 2,000,000,000.0                
Interest rate, stated percentage 6.00%                
5.125% Senior Notes Due 2025                  
Related Party Transaction [Line Items]                  
Interest rate, stated percentage   5.125%              
5.125% Senior Notes Due 2025 | DT | Sprint | Senior Notes                  
Related Party Transaction [Line Items]                  
Principal Issuances $ 1,250,000,000                
Interest rate, stated percentage 5.125%                
5.125% Senior Notes Due 2025 | Affiliates                  
Related Party Transaction [Line Items]                  
Interest rate, stated percentage             5.125%    
5.125% Senior Notes Due 2025 | Affiliates | Senior Notes                  
Related Party Transaction [Line Items]                  
Interest rate, stated percentage   5.125%              
5.375% Senior Notes Due 2027                  
Related Party Transaction [Line Items]                  
Interest rate, stated percentage   5.375%              
5.375% Senior Notes Due 2027 | DT | Sprint | Senior Notes                  
Related Party Transaction [Line Items]                  
Principal Issuances $ 1,250,000,000                
Interest rate, stated percentage 5.375%                
5.375% Senior Notes Due 2027 | Affiliates                  
Related Party Transaction [Line Items]                  
Interest rate, stated percentage   5.375%              
5.125% Senior Notes due 2021 | Affiliates | Senior Notes                  
Related Party Transaction [Line Items]                  
Principal Amount             $ 1,250,000,000    
Interest rate, stated percentage             5.125%