Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total Revenue	$ 1,730	$ 1,801	$ 5,246	$ 5,518
Adjustments for non-ASC 606 revenue	(122)	(118)	(359)	(360)
Total Revenue from Contracts with Customers	1,608	1,683	4,887	5,158
Voice and Other [Member]
Disaggregation of Revenue [Line Items]
Total Revenue	522	567	1,595	1,726
Adjustments for non-ASC 606 revenue	(83)	(87)	(251)	(263)
Total Revenue from Contracts with Customers	439	480	1,344	1,463
Fiber Infrastructure [Member]
Disaggregation of Revenue [Line Items]
Total Revenue	495	505	1,500	1,527
Adjustments for non-ASC 606 revenue	(30)	(30)	(90)	(94)
Total Revenue from Contracts with Customers	465	475	1,410	1,433
IP & Data Services [Member]
Disaggregation of Revenue [Line Items]
Total Revenue	118	128	357	389
Adjustments for non-ASC 606 revenue	0	0	0	0
Total Revenue from Contracts with Customers	118	128	357	389
Affiliate Services [Member]
Disaggregation of Revenue [Line Items]
Total Revenue	595	601	1,794	1,876
Adjustments for non-ASC 606 revenue	(9)	(1)	(18)	(3)
Total Revenue from Contracts with Customers	$ 586	$ 600	$ 1,776	$ 1,873