Receivables and Related Allowance for Credit Losses - Schedule of Equipment Installment Plan Receivables by Credit Category (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Financing Receivable, Credit Quality Indicator [Line Items]
EIP receivables, net of unamortized discount	$ 7,357	$ 8,060
Current - 30 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
EIP receivables, net of unamortized discount	7,163
31 - 60 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
EIP receivables, net of unamortized discount	85
61 - 90 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
EIP receivables, net of unamortized discount	56
More than 90 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
EIP receivables, net of unamortized discount	53
Prime
Financing Receivable, Credit Quality Indicator [Line Items]
Originated in 2026	3,638
Originated in 2025	2,222
Originated prior to 2025	255
EIP receivables, net of unamortized discount	6,115
Prime \| Current - 30 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Originated in 2026	3,589
Originated in 2025	2,182
Originated prior to 2025	247
EIP receivables, net of unamortized discount	6,018
Prime \| 31 - 60 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Originated in 2026	25
Originated in 2025	17
Originated prior to 2025	3
EIP receivables, net of unamortized discount	45
Prime \| 61 - 90 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Originated in 2026	13
Originated in 2025	12
Originated prior to 2025	2
EIP receivables, net of unamortized discount	27
Prime \| More than 90 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Originated in 2026	11
Originated in 2025	11
Originated prior to 2025	3
EIP receivables, net of unamortized discount	25
Subprime
Financing Receivable, Credit Quality Indicator [Line Items]
Originated in 2026	748
Originated in 2025	451
Originated prior to 2025	43
EIP receivables, net of unamortized discount	1,242
Subprime \| Current - 30 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Originated in 2026	696
Originated in 2025	411
Originated prior to 2025	38
EIP receivables, net of unamortized discount	1,145
Subprime \| 31 - 60 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Originated in 2026	23
Originated in 2025	15
Originated prior to 2025	2
EIP receivables, net of unamortized discount	40
Subprime \| 61 - 90 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Originated in 2026	16
Originated in 2025	12
Originated prior to 2025	1
EIP receivables, net of unamortized discount	29
Subprime \| More than 90 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Originated in 2026	13
Originated in 2025	13
Originated prior to 2025	2
EIP receivables, net of unamortized discount	$ 28

Financing Receivable, Before Allowance for Credit Loss, Net of Unamortized Discount

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