Wireless Licenses, Goodwill and Other Intangible Assets - Composition of Other Intangible Assets, Net (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross (1) Amount	$ 23,327	$ 27,477
Accumulated Amortization	(16,305)	(18,064)
Net Amount	7,022	9,413
Customer Lists
Finite-Lived Intangible Assets [Line Items]
Gross (1) Amount	1,933	4,021
Accumulated Amortization	(1,033)	(1,961)
Net Amount	$ 900	2,060
Customer Lists | Minimum
Finite-Lived Intangible Assets [Line Items]
Other intangible asset, useful life	8 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 (1) Amount	$ 20,525	21,685
Accumulated Amortization	(14,524)	(15,104)
Net Amount	$ 6,001	6,581
Non-Network Internal-Use Software | Minimum
Finite-Lived Intangible Assets [Line Items]
Other intangible asset, useful life	5 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 (1) Amount	$ 869	1,771
Accumulated Amortization	(748)	(999)
Net Amount	$ 121	$ 772
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