Acquisitions and Divestitures - Acquisitions (Details) - USD ($) $ in Millions		1 Months Ended	6 Months Ended			18 Months Ended
	Nov. 23, 2021	Feb. 28, 2021	Dec. 31, 2023	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2024
Business Acquisition [Line Items]
Payments for deposits				$ 1,085	$ 2,275
Business acquisition, purchase price in cash				0	(247)
Estimated fair value of the contingent consideration				202
Spectrum licenses | Spectrum Licenses, C-Band
Business Acquisition [Line Items]
Estimated clearing and incentive costs		$ 7,600
Spectrum licenses | Spectrum Licenses, C-Band | Scenario, Forecast
Business Acquisition [Line Items]
Estimated clearing and incentive costs			$ 4,200			$ 4,600
Spectrum licenses | Spectrum Licenses, C-Band | Projected Clearing Costs
Business Acquisition [Line Items]
Payments for deposits				114	1,400
Accrued clearing incentives and clearing costs				365
TracFone Wireless, Inc.
Business Acquisition [Line Items]
Business acquisition, purchase price in cash	$ 3,500
Number of shares issuable (in shares)	57,596,544
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	$ 3,000
Future cash consideration related to achievement of certain performance measures	650
Estimated fair value of the contingent consideration	$ 560
Contingent consideration, earn out period	2 years
Contingent consideration payment				$ 102
Cash proceeds from acquisition					$ 248