Equipment Installment Plans - Gross Receivables by Credit Category (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	$ 1,110	$ 1,151
2022	138
2023	358
2024	614
Unbilled \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	1,050	1,085
Billed \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	42	43
Billed \| Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	18	23
Lowest Risk
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	1,001	1,024
2022	131
2023	332
2024	538
Lowest Risk \| Unbilled \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	955	977
Lowest Risk \| Billed \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	36	35
Lowest Risk \| Billed \| Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	10	12
Lower Risk
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	86	100
2022	6
2023	22
2024	58
Lower Risk \| Unbilled \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	77	88
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	5	7
Slight Risk
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	16	21
2022	1
2023	3
2024	12
Slight Risk \| Unbilled \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	13	16
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	3
Higher Risk
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	7	6
2022	0
2023	1
2024	6
Higher Risk \| Unbilled \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	5	4
Higher Risk \| Billed \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	1	1
Higher Risk \| Billed \| Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	$ 1	$ 1

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