Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	$ 20,712	$ 21,458	$ 22,580
Adjustments for Non-ASC 606 Revenue	(1,915)	(1,953)	(1,538)
Total Revenue from Contracts with Customers	18,797	19,505	21,042
Goods and services transferred at a point in time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue from Contracts with Customers	250	221	230
Services performed over time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue from Contracts with Customers	18,547	19,284	20,812
IP and Data Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	6,372	6,621	6,614
Transport and Infrastructure
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	4,989	5,019	5,256
Voice and Collaboration
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	3,621	3,766	4,091
IT and Managed Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	479	535	625
Broadband
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	2,909	2,876	2,824
Voice
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	1,622	1,837	2,127
Other
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	105	172	316
Operating Segments
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	20,712	21,458	22,580
Operating Segments | IP and Data Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	6,372	6,621	6,614
Operating Segments | Transport and Infrastructure
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	4,989	5,019	5,256
Operating Segments | Voice and Collaboration
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	3,621	3,766	4,091
Operating Segments | IT and Managed Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	479	535	625
Operating Segments | Broadband
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	2,909	2,876	2,824
Operating Segments | Voice
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	1,622	1,837	2,127
Operating Segments | Other
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	105	172	316
Operating Segments | International and Global Accounts
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	3,405	3,476	3,543
Adjustments for Non-ASC 606 Revenue	(373)	(365)	(83)
Total Revenue from Contracts with Customers	3,032	3,111	3,460
Operating Segments | International and Global Accounts | IP and Data Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	1,556	1,627	1,682
Adjustments for Non-ASC 606 Revenue	0	0	0
Total Revenue from Contracts with Customers	1,556	1,627	1,682
Operating Segments | International and Global Accounts | Transport and Infrastructure
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	1,265	1,268	1,230
Adjustments for Non-ASC 606 Revenue	(373)	(365)	(83)
Total Revenue from Contracts with Customers	892	903	1,147
Operating Segments | International and Global Accounts | Voice and Collaboration
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	368	354	365
Adjustments for Non-ASC 606 Revenue	0	0	0
Total Revenue from Contracts with Customers	368	354	365
Operating Segments | International and Global Accounts | IT and Managed Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	216	227	266
Adjustments for Non-ASC 606 Revenue	0	0	0
Total Revenue from Contracts with Customers	216	227	266
Operating Segments | International and Global Accounts | Broadband
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | International and Global Accounts | Voice
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | International and Global Accounts | Other
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Enterprise
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	5,722	5,696	5,765
Adjustments for Non-ASC 606 Revenue	(138)	(134)	(43)
Total Revenue from Contracts with Customers	5,584	5,562	5,722
Operating Segments | Enterprise | IP and Data Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	2,474	2,538	2,485
Adjustments for Non-ASC 606 Revenue	(2)	0	0
Total Revenue from Contracts with Customers	2,472	2,538	2,485
Operating Segments | Enterprise | Transport and Infrastructure
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	1,608	1,479	1,484
Adjustments for Non-ASC 606 Revenue	(135)	(134)	(43)
Total Revenue from Contracts with Customers	1,473	1,345	1,441
Operating Segments | Enterprise | Voice and Collaboration
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	1,424	1,423	1,495
Adjustments for Non-ASC 606 Revenue	(1)	0	0
Total Revenue from Contracts with Customers	1,423	1,423	1,495
Operating Segments | Enterprise | IT and Managed Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	216	256	301
Adjustments for Non-ASC 606 Revenue	0	0	0
Total Revenue from Contracts with Customers	216	256	301
Operating Segments | Enterprise | Broadband
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Enterprise | Voice
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Enterprise | Other
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Small and Medium Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	2,557	2,727	2,918
Adjustments for Non-ASC 606 Revenue	(40)	(36)	(40)
Total Revenue from Contracts with Customers	2,517	2,691	2,878
Operating Segments | Small and Medium Business | IP and Data Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	1,062	1,091	1,078
Adjustments for Non-ASC 606 Revenue	(3)	0	0
Total Revenue from Contracts with Customers	1,059	1,091	1,078
Operating Segments | Small and Medium Business | Transport and Infrastructure
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	352	365	424
Adjustments for Non-ASC 606 Revenue	(34)	(36)	(40)
Total Revenue from Contracts with Customers	318	329	384
Operating Segments | Small and Medium Business | Voice and Collaboration
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	1,098	1,226	1,366
Adjustments for Non-ASC 606 Revenue	(3)	0	0
Total Revenue from Contracts with Customers	1,095	1,226	1,366
Operating Segments | Small and Medium Business | IT and Managed Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	45	45	50
Adjustments for Non-ASC 606 Revenue	0	0	0
Total Revenue from Contracts with Customers	45	45	50
Operating Segments | Small and Medium Business | Broadband
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Small and Medium Business | Voice
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Small and Medium Business | Other
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Wholesale
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	3,777	4,042	4,360
Adjustments for Non-ASC 606 Revenue	(517)	(545)	(397)
Total Revenue from Contracts with Customers	3,260	3,497	3,963
Operating Segments | Wholesale | IP and Data Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	1,280	1,365	1,369
Adjustments for Non-ASC 606 Revenue	0	0	0
Total Revenue from Contracts with Customers	1,280	1,365	1,369
Operating Segments | Wholesale | Transport and Infrastructure
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	1,764	1,907	2,118
Adjustments for Non-ASC 606 Revenue	(517)	(545)	(397)
Total Revenue from Contracts with Customers	1,247	1,362	1,721
Operating Segments | Wholesale | Voice and Collaboration
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	731	763	865
Adjustments for Non-ASC 606 Revenue	0	0	0
Total Revenue from Contracts with Customers	731	763	865
Operating Segments | Wholesale | IT and Managed Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	2	7	8
Adjustments for Non-ASC 606 Revenue	0	0	0
Total Revenue from Contracts with Customers	2	7	8
Operating Segments | Wholesale | Broadband
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Wholesale | Voice
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Wholesale | Other
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	5,251	5,517	5,994
Adjustments for Non-ASC 606 Revenue	(847)	(873)	(975)
Total Revenue from Contracts with Customers	4,404	4,644	5,019
Operating Segments | Consumer | IP and Data Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Consumer | Transport and Infrastructure
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Consumer | Voice and Collaboration
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Consumer | IT and Managed Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	0	0	0
Operating Segments | Consumer | Broadband
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	2,909	2,876	2,824
Adjustments for Non-ASC 606 Revenue	(217)	(215)	(213)
Total Revenue from Contracts with Customers	2,692	2,661	2,611
Operating Segments | Consumer | Voice
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	1,622	1,837	2,127
Adjustments for Non-ASC 606 Revenue	0	0	0
Total Revenue from Contracts with Customers	1,622	1,837	2,127
Operating Segments | Consumer | Regulatory
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	615	632	727
Adjustments for Non-ASC 606 Revenue	(615)	(632)	(727)
Total Revenue from Contracts with Customers	0	0	0
Operating Segments | Consumer | Other
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	105	172	316
Adjustments for Non-ASC 606 Revenue	(15)	(26)	(35)
Total Revenue from Contracts with Customers	$ 90	$ 146	$ 281