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Business Combination, Number Of Shares of Acquirer Stock Issued For Each Share Of Acquiree Stock

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Lease-out and Leaseback Transaction, Renewal Options, Term

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Payments for Asset Acquisitions

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Spectrum Leasing, Lease Term

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Spectrum Leasing, Number of Automatic Renewal Provisions

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Spectrum Leasing, Total Lease Term

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Amount of allowance for credit loss on accounts receivable.

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Summary of Significant Accounting Policies - Narrative (Details) $ in Millions				3 Months Ended			6 Months Ended		12 Months Ended
	Jul. 01, 2020 USD ($)	Apr. 01, 2020 USD ($) provision	Apr. 29, 2018 shares	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2005 USD ($) tower_site	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Device upgrade period							18 months
Revenues				$ 17,671		$ 10,979	$ 28,784	$ 22,059
Accumulated deficit				$ 7,839			$ 7,839				$ 8,833
Total imputed discount and allowance rate				7.80%			7.80%				7.00%
Postpaid revenues
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Remaining contract duration (in years)							24 months
Revenues				$ 9,959		5,613	$ 15,846	11,106
Roaming and other service revenues \| Reclassification
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues					$ 133	$ 120		$ 234
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Remaining contract duration (in years)							1 year
Minimum \| Wireline Revenue
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Remaining contract duration (in years)							24 months
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Remaining contract duration (in years)							10 years
Maximum \| Wireline Revenue
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Remaining contract duration (in years)							36 months
Maximum \| EIP Securitization Arrangement
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equipment installment plan, maximum payment term							24 months
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
DISH
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Initial term of leaseback									10 years
Renewal option term									5 years
Sprint
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of communications towers \| tower_site									6,600
Term of lease-out									32 years
Upfront proceeds received									$ 1,200
Prepaid Business \| T-Mobile and Sprint \| DISH \| Subsequent Event
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
Automatic renewal provisions \| provision		2
Deferred tax assets		$ 1,100
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