Equipment Installment Plans - EIP Receivables (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Equipment installment plan receivables, gross	$ 1,127	$ 1,211
Allowance for credit losses	(85)	(96)
Equipment installment plan receivables, net	1,042	1,115
Accounts receivable — Customers and agents (Current portion)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Equipment installment plan receivables, net	581	646
Other assets and deferred charges (Non-current portion)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Equipment installment plan receivables, net	$ 461	$ 469