Revenue Recognition (Disaggregation Of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,593	$ 1,843
Subsidy and other revenue	83	90
Total revenue	1,676	1,933
Lease revenue	16	17
Revenue, Remaining Performance Obligation, Amount	2,419
Data And Internet Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	842	932
Voice Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	487	572
Video Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	169	222
Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	95	117
Consumer [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	844	971
Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 749	$ 872