Summary of Significant Accounting Policies - Government Assistance and Advertising Costs (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Sep. 30, 2024 |
Sep. 30, 2025 |
Sep. 30, 2024 |
Dec. 31, 2024 |
Dec. 31, 2023 |
|
| Summary of Significant Accounting Policies | ||||||
| Grant proceeds received for capital expenditures | $ 22 | $ 40 | $ 54 | $ 6 | ||
| Advertising costs | 7 | 5 | ||||
| Federal government grants to construct broadband | ||||||
| Summary of Significant Accounting Policies | ||||||
| Grant proceeds received for capital expenditures | $ 3 | $ 21 | $ 22 | $ 40 | 54 | 6 |
| Short-term deferred revenue | 3 | 2 | ||||
| Long-term deferred revenue | $ 92 | $ 41 | ||||
| Federal government grants to construct broadband | Minimum | ||||||
| Summary of Significant Accounting Policies | ||||||
| Government assistance transaction duration | 10 years | 11 years | ||||
| Federal government grants to construct broadband | Maximum | ||||||
| Summary of Significant Accounting Policies | ||||||
| Government assistance transaction duration | 22 years | 17 years | ||||