Sales Of Receivables (Finance Receivables Repurchased) (Details) - Equipment Installment - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value of repurchased receivables	$ 1,271	$ 1,418	$ 1,480
Carrying value of deferred purchase price	1,235	1,350	1,393
Gain on repurchases	$ 36	$ 68	$ 87

Amount, during period, representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date. Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. Excludes amounts related to receivables held-for-sale.

No definition available.

Name:	t_NotesReceivableGrossDuringPeriod
Namespace Prefix:	t_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration