Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications	$ (184)	$ 1,439	$ 1,342
Amounts reclassified from accumulated OCI	(1,321)	(1,905)	(1,924)
Other comprehensive income (loss) attributable to AT&T	(1,505)	(466)	(763)
Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income, beginning balance	2,300	2,766	3,529
Other comprehensive income (loss) attributable to AT&T	(1,505)	(466)	(763)
Accumulated other comprehensive income, ending balance	795	2,300	2,766
Foreign Currency Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income, beginning balance	(1,337)	(1,800)	(1,964)
Other comprehensive income (loss) before reclassifications	(545)	463	346
Amounts reclassified from accumulated OCI	127	0	0
Other comprehensive income (loss) attributable to AT&T	(418)	463	164
Accumulated other comprehensive income, ending balance	(1,755)	(1,337)	(1,800)
Net Unrealized Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income, beginning balance	(57)	(90)	45
Other comprehensive income (loss) before reclassifications	(19)	22	(143)
Amounts reclassified from accumulated OCI	30	11	8
Other comprehensive income (loss) attributable to AT&T	11	33	(135)
Accumulated other comprehensive income, ending balance	(46)	(57)	(90)
Net Unrealized Gains (Losses) on Derivative Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income, beginning balance	(1,029)	(1,998)	(1,422)
Other comprehensive income (loss) before reclassifications	380	922	(648)
Amounts reclassified from accumulated OCI	45	47	96
Other comprehensive income (loss) attributable to AT&T	425	969	(576)
Accumulated other comprehensive income, ending balance	(604)	(1,029)	(1,998)
Defined Benefit Postretirement Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive income, beginning balance	4,723	6,654	6,870
Other comprehensive income (loss) before reclassifications	0	32	1,787
Amounts reclassified from accumulated OCI	(1,523)	(1,963)	(2,028)
Other comprehensive income (loss) attributable to AT&T	(1,523)	(1,931)	(216)
Accumulated other comprehensive income, ending balance	$ 3,200	4,723	$ 6,654
Reclassification out of Accumulated Other Comprehensive Income [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated OCI		181
Reclassification out of Accumulated Other Comprehensive Income [Member] | Foreign Currency Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated OCI		182
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Unrealized Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated OCI		0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Unrealized Gains (Losses) on Derivative Instruments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated OCI		24
Reclassification out of Accumulated Other Comprehensive Income [Member] | Defined Benefit Postretirement Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated OCI		$ (25)