Equipment Installment Plans - EIP Receivables (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Equipment installment plan receivables, gross	$ 964	$ 1,008
Allowance for credit losses	(90)	(84)
Equipment installment plan receivables, net	874	924
Accounts receivable — Customers and agents (Current portion)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Equipment installment plan receivables, net	566	587
Other assets and deferred charges (Non-current portion)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Equipment installment plan receivables, net	$ 308	$ 337

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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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