Acquisitions and Divestitures (Details) numberOfCustomers in Thousands, $ in Millions	1 Months Ended					3 Months Ended			9 Months Ended		10 Months Ended
	Oct. 27, 2020 numberOfCounties numberOfCustomers	Sep. 30, 2020 USD ($) license shares	May 31, 2020 USD ($)	Mar. 31, 2020 USD ($) license	Dec. 31, 2019 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)
Business Acquisition [Line Items]
Number of licenses acquired | license				4,940
Payments for deposits									$ 1,987	$ 299
Gain (loss) on disposition of licenses, pre-tax						$ 0		$ 0	(1,195)	$ 0
Goodwill		$ 24,799			$ 24,389	24,799			24,799		$ 24,799
Spectrum licenses
Business Acquisition [Line Items]
Payments for deposits					$ 101						1,600
Spectrum licenses
Business Acquisition [Line Items]
Price payable for acquisitions				$ 3,400
Portion of price to be settled with 39 GHz licenses				$ 1,800
Gain (loss) on disposition of licenses, pre-tax									(1,200)
Gain (loss) on disposition of licenses									(914)
Average remaining renewal period of wireless license portfolio (in years)							9 years 10 months 24 days
Priority Access Licenses
Business Acquisition [Line Items]
Number of licenses acquired | license		557
Payments for deposits		$ 1,900
Various Other Wireless Licenses | Spectrum licenses
Business Acquisition [Line Items]
Payments for deposits						116			293
Blue Jeans Network
Business Acquisition [Line Items]
Price payable for acquisitions			$ 397
Goodwill			296
Intangible assets other than goodwill			$ 192
TracFone Wireless, Inc.
Business Acquisition [Line Items]
Cash payment to acquire business		3,100
Common stock value consideration to acquire business		3,100
Future cash consideration related to achievement of certain performance measures		$ 650				$ 650			650		$ 650
TracFone Wireless, Inc. | Minimum
Business Acquisition [Line Items]
Number of shares issuable (in shares) | shares		47,124,445
TracFone Wireless, Inc. | Maximum
Business Acquisition [Line Items]
Number of shares issuable (in shares) | shares		57,596,544
Bluegrass Cellular, Certain Assets | Subsequent Event
Business Acquisition [Line Items]
Number of customers | numberOfCustomers	210
Number of counties customers are serviced | numberOfCounties	34
Other Acquisitions
Business Acquisition [Line Items]
Cash payment to acquire business									$ 113