Fair Value Measurements (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
7.0% Senior Notes
Financial Instruments
Interest rate	7.00%
6.875% Senior Notes
Financial Instruments
Interest rate	6.875%
6.625% Senior Notes
Financial Instruments
Interest rate	6.625%
5.875% Senior Notes
Financial Instruments
Interest rate	5.875%
7.25% 2063 Senior Notes | UScellular
Financial Instruments
Interest rate	7.25%
7.25% 2064 Senior Notes | UScellular
Financial Instruments
Interest rate	7.25%
6.25% Senior Notes | UScellular
Financial Instruments
Interest rate	6.25%
6.95% Senior Notes | UScellular
Financial Instruments
Interest rate	6.95%
6.7% Senior Notes | UScellular
Financial Instruments
Interest rate	6.70%
5.5% Senior Notes | UScellular
Financial Instruments
Interest rate	5.50%
Book Value | Retail
Financial Instruments
Long-term debt	$ 2,753	$ 2,753
Book Value | Institutional
Financial Instruments
Long-term debt	535	535
Book Value | Other
Financial Instruments
Long-term debt	796	230
Fair Value | Level 2 | Retail
Financial Instruments
Long-term debt	2,814	2,809
Fair Value | Level 2 | Institutional
Financial Instruments
Long-term debt	661	707
Fair Value | Level 2 | Other
Financial Instruments
Long-term debt	$ 796	$ 230
Interest rate | Institutional and Other | Minimum
Financial Instruments
Fair value assumption, interest rate	1.31%	1.35%
Interest rate | Institutional and Other | Maximum
Financial Instruments
Fair value assumption, interest rate	4.48%	3.75%