Wireless Licenses, Goodwill and Other Intangible Assets - Composition of Other Intangible Assets, Net (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 24,646	$ 24,105
Accumulated Amortization	(14,785)	(13,858)
Net Amount	9,861	10,247
Customer Lists
Finite-Lived Intangible Assets [Line Items]
Gross Amount	3,623	3,621
Accumulated Amortization	(860)	(691)
Net Amount	$ 2,763	2,930
Customer Lists | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life for finite-lived intangible assets	8 years
Customer Lists | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life for finite-lived intangible assets	13 years
Non-Network Internal-Use Software
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 18,540	18,010
Accumulated Amortization	(13,017)	(12,374)
Net Amount	$ 5,523	5,636
Non-Network Internal-Use Software | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life for finite-lived intangible assets	3 years
Non-Network Internal-Use Software | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life for finite-lived intangible assets	7 years
Other
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 2,483	2,474
Accumulated Amortization	(908)	(793)
Net Amount	$ 1,575	$ 1,681
Other | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life for finite-lived intangible assets	2 years
Other | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life for finite-lived intangible assets	25 years