Summary Of Significant Accounting Policies (Schedule Of Revenues From External Customers) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 2,251	$ 2,524	$ 6,911	$ 6,487
Customer Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	2,060	2,319	6,325	5,889
Switched Access And Subsidy Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	191	205	586	598
Data And Internet Services [Member] | Customer Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	956	1,045	2,923	2,680
Voice Services [Member] | Customer Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	702	809	2,177	2,112
Video Services [Member] | Customer Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	318	392	994	879
Other [Member] | Customer Revenue [Member]
Segment Reporting Information [Line Items]
Revenues	$ 84	$ 73	$ 231	$ 218