Consolidated Statement Of Changes In Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Preferred Stock Preferred Stock - Series A	Preferred Stock Preferred Stock - Series B	Preferred Stock Preferred Stock - Series C	Common Stock	Additional Paid-In Capital	Additional Paid-In Capital Preferred Stock	Additional Paid-In Capital Common Stock	Retained Earnings	Retained Earnings Cumulative effect of accounting change and other adjustments	Retained Earnings Adjusted beginning balance	Treasury Stock	Accumulated Other Comprehensive Income Attributable to AT&T, net of tax	Noncontrolling Interest	Noncontrolling Interest Cumulative effect of accounting change and other adjustments	Noncontrolling Interest Adjusted beginning balance
Balance at beginning of period at Dec. 31, 2018	$ 193,884	$ 0	$ 0	$ 0	$ 7,621	$ 125,525			$ 58,753	$ 316	$ 59,069	$ (12,059)	$ 4,249	$ 9,795	$ 29	$ 9,824
Balance at beginning of period (in shares) at Dec. 31, 2018		0	0	0	7,621							(339)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase and acquisition of common stock								$ 0
Issuance of stock		$ 0	$ 0	$ 0	$ 0		$ 0
Issuance of stock (in shares)		0	0	0	0
Repurchase and acquisition of common stock												$ (466)
Repurchase and acquisition of common stock (in shares)												(14)
Issuance of treasury stock						(128)						$ 1,330
Issuance of treasury stock, (in shares)												36
Share-based payments						(258)
Changes related to acquisition of interests held by noncontrolling owners						0
Net income attributable to AT&T	11,509								11,509
Preferred stock dividends									0
Common stock dividends ( $0.52, $0.51, $1.56, and $1.53 per share)									(11,231)
Other comprehensive income attributable to AT&T	(2,112)												(2,112)
Net income attributable to noncontrolling interest	762													762
Issuance and acquisition of noncontrolling owners														1,498
Distributions														(791)
Translation adjustments attributable to noncontrolling interest, net of taxes	(15)													(15)
Balance at end of period at Sep. 30, 2019	194,327	$ 0	$ 0	$ 0	$ 7,621	125,139			59,347			$ (11,195)	2,137	11,278
Balance at end of period (in shares) at Sep. 30, 2019		0	0	0	7,621							(317)
Balance at beginning of period at Jun. 30, 2019	194,081	$ 0	$ 0	$ 0	$ 7,621	125,109			59,389	0	59,389	$ (11,151)	3,289	9,824	0	9,824
Balance at beginning of period (in shares) at Jun. 30, 2019		0	0	0	7,621							(316)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase and acquisition of common stock								0
Issuance of stock		$ 0	$ 0	$ 0	$ 0		0
Issuance of stock (in shares)		0	0	0	0
Repurchase and acquisition of common stock												$ (186)
Repurchase and acquisition of common stock (in shares)												(5)
Issuance of treasury stock						(1)						$ 142
Issuance of treasury stock, (in shares)												4
Share-based payments						31
Changes related to acquisition of interests held by noncontrolling owners						0
Net income attributable to AT&T	3,700								3,700
Preferred stock dividends									0
Common stock dividends ( $0.52, $0.51, $1.56, and $1.53 per share)									(3,742)
Other comprehensive income attributable to AT&T													(1,152)
Net income attributable to noncontrolling interest	249													249
Issuance and acquisition of noncontrolling owners														1,488
Distributions														(266)
Translation adjustments attributable to noncontrolling interest, net of taxes	(17)													(17)
Balance at end of period at Sep. 30, 2019	194,327	$ 0	$ 0	$ 0	$ 7,621	125,139			59,347			$ (11,195)	2,137	11,278
Balance at end of period (in shares) at Sep. 30, 2019		0	0	0	7,621							(317)
Balance at beginning of period at Dec. 31, 2019	201,934	$ 0	$ 0	$ 0	$ 7,621	126,279			57,936	(293)	57,643	$ (13,085)	5,470	17,713	(7)	17,706
Balance at beginning of period (in shares) at Dec. 31, 2019		0	0	0	7,621							(366)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase and acquisition of common stock								67
Issuance of stock		$ 0	$ 0	$ 0	$ 0		3,869
Issuance of stock (in shares)		0	0	0	0
Repurchase and acquisition of common stock												$ (5,600)
Repurchase and acquisition of common stock (in shares)												(149)
Issuance of treasury stock						(56)						$ 735
Issuance of treasury stock, (in shares)												19
Share-based payments						(24)
Changes related to acquisition of interests held by noncontrolling owners						4
Net income attributable to AT&T	8,707								8,707
Preferred stock dividends									(103)
Common stock dividends ( $0.52, $0.51, $1.56, and $1.53 per share)									(11,153)
Other comprehensive income attributable to AT&T	(4,821)												(4,821)
Net income attributable to noncontrolling interest	987													987
Issuance and acquisition of noncontrolling owners														1,979
Distributions														(1,108)
Translation adjustments attributable to noncontrolling interest, net of taxes	(61)													(61)
Balance at end of period at Sep. 30, 2020	195,056	$ 0	$ 0	$ 0	$ 7,621	130,139			55,094			$ (17,950)	649	19,503
Balance at end of period (in shares) at Sep. 30, 2020		0	0	0	7,621							(496)
Balance at beginning of period at Jun. 30, 2020	193,453	$ 0	$ 0	$ 0	$ 7,621	130,046			56,045	$ 0	$ 56,045	$ (17,945)	129	17,557	$ 0	$ 17,557
Balance at beginning of period (in shares) at Jun. 30, 2020		0	0	0	7,621							(495)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase and acquisition of common stock								$ 0
Issuance of stock		$ 0	$ 0	$ 0	$ 0		$ 0
Issuance of stock (in shares)		0	0	0	0
Repurchase and acquisition of common stock												$ (19)
Repurchase and acquisition of common stock (in shares)												(1)
Issuance of treasury stock						(2)						$ 14
Issuance of treasury stock, (in shares)												0
Share-based payments						91
Changes related to acquisition of interests held by noncontrolling owners						4
Net income attributable to AT&T	2,816								2,816
Preferred stock dividends									(35)
Common stock dividends ( $0.52, $0.51, $1.56, and $1.53 per share)									(3,732)
Other comprehensive income attributable to AT&T													520
Net income attributable to noncontrolling interest	352													352
Issuance and acquisition of noncontrolling owners														1,978
Distributions														(382)
Translation adjustments attributable to noncontrolling interest, net of taxes	(2)													(2)
Balance at end of period at Sep. 30, 2020	$ 195,056	$ 0	$ 0	$ 0	$ 7,621	$ 130,139			$ 55,094			$ (17,950)	$ 649	$ 19,503
Balance at end of period (in shares) at Sep. 30, 2020		0	0	0	7,621							(496)