Revenue Recognition (Disaggregation Of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,627	$ 1,906	$ 5,175	$ 5,887
Subsidy and other revenue	99	91	285	278
Total revenue	1,726	1,997	5,460	6,165
Lease revenue	16	17	50	52
Transition services revenue	15		25
Revenue from contracts with customers, performance obligation	2,982		2,982
Data And Internet Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	838	928	2,644	2,858
Voice Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	500	621	1,595	1,900
Video services [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	186	244	608	772
Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	103	113	328	357
Consumer [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	859	1,024	2,729	3,151
Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 768	$ 882	$ 2,446	$ 2,736