Sales Of Receivables (Equipment Installment and AT&T Revolving Programs) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Equipment Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross receivable	$ 4,241	$ 4,576
Other Assets	1,570	1,632
Outstanding portfolio of receivables derecognized from our consolidated balance sheets	8,238	9,713
Cash proceeds received, net of remittances	5,944	7,211
Equipment Installment | Notes receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	2,190	2,467
Equipment Installment | Trade receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	481	477
Revolving
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross receivable	3,516	3,324
Other Assets	187	515
Outstanding portfolio of receivables derecognized from our consolidated balance sheets	5,100	4,300
Cash proceeds received, net of remittances	5,100	4,300
Revolving | Notes receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	0	0
Revolving | Trade receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 3,329	$ 2,809