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Debt - Financing Arrangements and Revolving Credit Facility (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Debt Instrument [Line Items]      
Short-term debt $ 25,000,000    
Issuance of short-term debt 2,340,000,000 $ 6,265,000,000 $ 2,910,000,000
Repayments of vendor financing arrangements 775,000,000 300,000,000 $ 300,000,000
Revolving Credit Facility [$2.5B] | Affiliated Entity      
Debt Instrument [Line Items]      
Revolving credit facility 2,500,000,000    
Revolving Credit Facility [$2.5B] | Unsecured Revolving Credit Facility | Affiliated Entity      
Debt Instrument [Line Items]      
Revolving credit facility 1,000,000,000.0    
Line of Credit | Revolving Credit Facility [$2.5B] | Secured Revolving Credit Facility | Affiliated Entity | Deutsche Telekom AG      
Debt Instrument [Line Items]      
Outstanding borrowings 0 0  
Line of Credit | Revolving Credit Facility [$1.5B] | Secured Revolving Credit Facility | Affiliated Entity | Deutsche Telekom AG      
Debt Instrument [Line Items]      
Financing commitment, amount 1,500,000,000    
Handset Financing Arrangement      
Debt Instrument [Line Items]      
Borrowing capacity 108,000,000    
Short-term debt 0 0  
Vendor Financing Arrangement      
Debt Instrument [Line Items]      
Short-term debt   $ 0  
Issuance of short-term debt 800,000,000    
Repayments of vendor financing arrangements $ 775,000,000