Goodwill, Spectrum License Transactions and Other Intangible Assets - Spectrum Licenses (Details) $ in Millions	1 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($) license	Feb. 28, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 31, 2018 USD ($)
Indefinite-lived Intangible Assets [Roll Forward]
Purchase of spectrum licenses			$ 967	$ 127	$ 5,828
Iowa Wireless
Indefinite-lived Intangible Assets [Roll Forward]
Spectrum licenses				87
Licensing Agreements
Indefinite-lived Intangible Assets [Roll Forward]
Beginning balance			35,559	35,366
Spectrum license acquisitions			857	138
Spectrum licenses transferred to held for sale			0	(1)
Costs to clear spectrum			49	56
Ending balance			$ 36,465	35,559	$ 35,366
Number of licenses | license	2,211
Purchase of spectrum licenses	$ 842			$ 50
Licensing Agreements | 28 GHz Auction
Indefinite-lived Intangible Assets [Roll Forward]
Purchase of spectrum licenses		$ 19
Asset purchase deposit						$ 20
Licensing Agreements | 24 GHz Auction
Indefinite-lived Intangible Assets [Roll Forward]
Purchase of spectrum licenses	$ 656
Asset purchase deposit		$ 147