Equipment Installment Plans - Gross Receivables by Credit Category (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	$ 1,127	$ 1,211
2020	1
2021	104
2022	530
2023	492
Unbilled
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	1,064	1,141
Billed \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	42	48
Billed \| Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	21	22
Lowest Risk
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	1,000	1,070
2020	1
2021	97
2022	480
2023	422
Lowest Risk \| Unbilled
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	952	1,016
Lowest Risk \| Billed \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	36	41
Lowest Risk \| Billed \| Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	12	13
Lower Risk
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	98	109
2020	0
2021	6
2022	41
2023	51
Lower Risk \| Unbilled
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	88	98
Lower Risk \| Billed \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	4	5
Lower Risk \| Billed \| Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	6	6
Slight Risk
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	21	26
2020	0
2021	1
2022	7
2023	13
Slight Risk \| Unbilled
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	18	22
Slight Risk \| Billed \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	1	2
Slight Risk \| Billed \| Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	2	2
Higher Risk
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	8	6
2020	0
2021	0
2022	2
2023	6
Higher Risk \| Unbilled
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	6	5
Higher Risk \| Billed \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	1	0
Higher Risk \| Billed \| Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	$ 1	$ 1

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