Segment Information - Operating Financial Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Operating Revenues	$ 32,607	$ 31,717	$ 96,582	$ 92,079
Operating Income (Loss)	7,675	6,988	21,641	21,964
Wireless equipment
Segment Reporting Information [Line Items]
Operating Revenues	5,353	4,352	15,437	12,414
External Operating Revenues
Segment Reporting Information [Line Items]
Operating Revenues	30,006	28,916	88,698	85,833
External Operating Revenues | Wireless
Segment Reporting Information [Line Items]
Operating Revenues	22,890	21,503	67,070	63,488
External Operating Revenues | Wireless | Service
Segment Reporting Information [Line Items]
Operating Revenues	15,949	15,823	47,062	47,158
External Operating Revenues | Wireless | Wireless equipment
Segment Reporting Information [Line Items]
Operating Revenues	5,353	4,352	15,437	12,414
External Operating Revenues | Wireless | Other
Segment Reporting Information [Line Items]
Operating Revenues	1,588	1,328	4,571	3,916
External Operating Revenues | Wireline
Segment Reporting Information [Line Items]
Operating Revenues	7,116	7,413	21,628	22,345
External Operating Revenues | Wireline | Consumer Markets
Segment Reporting Information [Line Items]
Operating Revenues	3,138	3,203	9,418	9,588
External Operating Revenues | Wireline | Enterprise Solutions
Segment Reporting Information [Line Items]
Operating Revenues	2,170	2,262	6,620	6,881
External Operating Revenues | Wireline | Partner Solutions
Segment Reporting Information [Line Items]
Operating Revenues	914	997	2,840	2,993
External Operating Revenues | Wireline | Business Markets
Segment Reporting Information [Line Items]
Operating Revenues	839	903	2,562	2,700
External Operating Revenues | Wireline | Other
Segment Reporting Information [Line Items]
Operating Revenues	55	48	188	183
Intersegment Eliminations
Segment Reporting Information [Line Items]
Operating Revenues	338	326	1,011	970
Intersegment Eliminations | Wireless
Segment Reporting Information [Line Items]
Operating Revenues	85	77	253	252
Intersegment Eliminations | Wireline
Segment Reporting Information [Line Items]
Operating Revenues	253	249	758	718
Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	30,344	29,242	89,709	86,803
Operating Income (Loss)	8,461	7,668	24,834	22,407
Operating Segments | Wireless
Segment Reporting Information [Line Items]
Operating Revenues	22,973	21,580	67,322	63,740
Operating Income (Loss)	8,511	7,603	24,834	22,089
Operating Segments | Wireline
Segment Reporting Information [Line Items]
Operating Revenues	7,371	7,662	22,387	23,063
Operating Income (Loss)	$ (50)	$ 65	$ 0	$ 318