v3.25.3
Summary of Significant Accounting Policies - Disaggregation of revenue (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
Revenue Recognition            
Revenue $ 257 $ 262 $ 784 $ 753 $ 1,016 $ 981
Consumer Revenue, Data            
Revenue Recognition            
Revenue         246 245
Consumer Revenue, Wireless            
Revenue Recognition            
Revenue         142 145
Consumer Revenue, Other            
Revenue Recognition            
Revenue         44 45
Business Revenue, Data            
Revenue Recognition            
Revenue         457 412
Business Revenue, Wireless            
Revenue Recognition            
Revenue         40 43
Business Revenue, Other            
Revenue Recognition            
Revenue         11 14
Lease, grant, and revenue from subsidies            
Revenue Recognition            
Revenue         $ 76 $ 77