Wireless Licenses, Goodwill and Other Intangible Assets - Composition of Other Intangible Assets, Net (Detail) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 35,495	$ 35,042
Accumulated Amortization	(24,648)	(23,913)
Net Amount	10,847	11,129
Customer Lists
Finite-Lived Intangible Assets [Line Items]
Gross Amount	4,242	4,242
Accumulated Amortization	(2,751)	(2,629)
Net Amount	$ 1,491	1,613
Customer Lists | Minimum
Finite-Lived Intangible Assets [Line Items]
Other intangible asset, useful life	6 years
Customer Lists | Maximum
Finite-Lived Intangible Assets [Line Items]
Other intangible asset, useful life	13 years
Non-Network Internal-Use Software
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 28,587	28,136
Accumulated Amortization	(20,291)	(19,743)
Net Amount	$ 8,296	8,393
Non-Network Internal-Use Software | Minimum
Finite-Lived Intangible Assets [Line Items]
Other intangible asset, useful life	3 years
Non-Network Internal-Use Software | Maximum
Finite-Lived Intangible Assets [Line Items]
Other intangible asset, useful life	7 years
Other
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 2,666	2,664
Accumulated Amortization	(1,606)	(1,541)
Net Amount	$ 1,060	$ 1,123
Other | Minimum
Finite-Lived Intangible Assets [Line Items]
Other intangible asset, useful life	4 years
Other | Maximum
Finite-Lived Intangible Assets [Line Items]
Other intangible asset, useful life	25 years