Equipment Installment Plans - Gross Receivables by Credit Category (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	$ 1,032	$ 1,110
2022	42
2023	227
2024	465
2025	298
Unbilled
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	969	1,050
Billed \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	45	42
Billed \| Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	18	18
Lowest Risk
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	933	1,001
2022	40
2023	214
2024	420
2025	259
Lowest Risk \| Unbilled
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	883	955
Lowest Risk \| Billed \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	39	36
Lowest Risk \| Billed \| Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	11	10
Lower Risk
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	77	86
2022	2
2023	12
2024	34
2025	29
Lower Risk \| Unbilled
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	68	77
Lower Risk \| Billed \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	4	4
Lower Risk \| Billed \| Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	5	5
Slight Risk
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	14	16
2022	0
2023	1
2024	6
2025	7
Slight Risk \| Unbilled
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	12	13
Slight Risk \| Billed \| Current
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	1	1
Slight Risk \| Billed \| Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	1	2
Higher Risk
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	8	7
2022	0
2023	0
2024	5
2025	3
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	1
Higher Risk \| Billed \| Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Equipment installment plan receivables, gross	$ 1	$ 1

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