Segment Information - Operating Financial Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Operating Revenues	$ 32,203	$ 30,548	$ 63,975	$ 60,362
Operating Income (Loss)	6,617	8,014	13,966	14,976
Wireless equipment
Segment Reporting Information [Line Items]
Operating Revenues	5,044	4,298	10,084	8,062
External Operating Revenues
Segment Reporting Information [Line Items]
Operating Revenues	29,577	28,702	58,690	56,917
External Operating Revenues | Wireless
Segment Reporting Information [Line Items]
Operating Revenues	22,373	21,209	44,180	41,985
External Operating Revenues | Wireless | Service
Segment Reporting Information [Line Items]
Operating Revenues	15,741	15,605	31,113	31,335
External Operating Revenues | Wireless | Wireless equipment
Segment Reporting Information [Line Items]
Operating Revenues	5,044	4,298	10,084	8,062
External Operating Revenues | Wireless | Other
Segment Reporting Information [Line Items]
Operating Revenues	1,588	1,306	2,983	2,588
External Operating Revenues | Wireline
Segment Reporting Information [Line Items]
Operating Revenues	7,204	7,493	14,510	14,932
External Operating Revenues | Wireline | Consumer Markets
Segment Reporting Information [Line Items]
Operating Revenues	3,131	3,184	6,280	6,385
External Operating Revenues | Wireline | Enterprise Solutions
Segment Reporting Information [Line Items]
Operating Revenues	2,210	2,308	4,450	4,619
External Operating Revenues | Wireline | Partner Solutions
Segment Reporting Information [Line Items]
Operating Revenues	947	1,007	1,926	1,996
External Operating Revenues | Wireline | Business Markets
Segment Reporting Information [Line Items]
Operating Revenues	851	917	1,722	1,796
External Operating Revenues | Wireline | Other
Segment Reporting Information [Line Items]
Operating Revenues	65	77	132	136
Intersegment Eliminations
Segment Reporting Information [Line Items]
Operating Revenues	331	299	675	644
Intersegment Eliminations | Wireless
Segment Reporting Information [Line Items]
Operating Revenues	76	73	169	175
Intersegment Eliminations | Wireline
Segment Reporting Information [Line Items]
Operating Revenues	255	226	506	469
Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	29,908	29,001	59,365	57,561
Operating Income (Loss)	8,255	7,457	16,373	14,739
Operating Segments | Wireless
Segment Reporting Information [Line Items]
Operating Revenues	22,449	21,282	44,349	42,160
Operating Income (Loss)	8,274	7,410	16,323	14,486
Operating Segments | Wireline
Segment Reporting Information [Line Items]
Operating Revenues	7,459	7,719	15,016	15,401
Operating Income (Loss)	$ (19)	$ 47	$ 50	$ 253