Wireless Licenses, Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Indefinite-lived Intangible Assets [Line Items]
Gain (loss) on disposition of licenses, pre-tax	$ 0	$ 0	$ (1,195)	$ 0
Wireless licenses	95,958		95,958				$ 95,059
Wireless Licenses
Indefinite-lived Intangible Assets [Line Items]
Wireless licenses under development	$ 6,900	$ 6,500	6,900	6,500
Interest costs capitalized			$ 171	$ 248
Assets held-for-sale						$ 2,800
Average remaining renewal period of wireless license portfolio (in years)			10 years
Spectrum Licenses, 39 GHz
Indefinite-lived Intangible Assets [Line Items]
Gain (loss) on disposition of licenses, pre-tax			$ (1,200)
Gain (loss) on disposition of licenses			$ (914)
Wireless licenses					$ 3,400
Disposal Group, Held-for-sale, Not Discontinued Operations | Spectrum licenses
Indefinite-lived Intangible Assets [Line Items]
Intangible assets held-for-sale						$ 1,600