Revenue Recognition - Disaggregation of revenue (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total operating revenue		$ 2,113	$ 2,149	$ 2,101	$ 2,130	$ 2,114	$ 2,141	$ 2,133	$ 2,162	$ 8,493		$ 8,550	$ 8,910
Adjustments for Non-ASC 606 Revenue	[1]									(531)
Total Revenue from Contracts with Customers										7,962
Goods and services transferred at a point in time
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers										69
Services performed over time
Disaggregation of Revenue [Line Items]
Total Revenue from Contracts with Customers										7,893
IP and Data Services
Disaggregation of Revenue [Line Items]
Total operating revenue										616	[2]	634	667
Adjustments for Non-ASC 606 Revenue	[1],[2]									0
Total Revenue from Contracts with Customers	[2]									616
Transport and Infrastructure
Disaggregation of Revenue [Line Items]
Total operating revenue										2,926	[3]	3,006	3,109
Adjustments for Non-ASC 606 Revenue	[1],[3]									(321)
Total Revenue from Contracts with Customers	[3]									2,605
Voice and Collaboration
Disaggregation of Revenue [Line Items]
Total operating revenue										1,800	[4]	1,980	2,252
Adjustments for Non-ASC 606 Revenue	[1],[4]									0
Total Revenue from Contracts with Customers	[4]									1,800
IT and Managed Services
Disaggregation of Revenue [Line Items]
Total operating revenue										6	[5]	0	2
Adjustments for Non-ASC 606 Revenue	[1],[5]									0
Total Revenue from Contracts with Customers	[5]									6
Regulatory Services
Disaggregation of Revenue [Line Items]
Total operating revenue										210	[6]	211	217
Adjustments for Non-ASC 606 Revenue	[1],[6]									(210)
Total Revenue from Contracts with Customers	[6]									0
Affiliate revenue
Disaggregation of Revenue [Line Items]
Total operating revenue										2,935	[7]	$ 2,719	$ 2,663
Adjustments for Non-ASC 606 Revenue	[1],[7]									0
Total Revenue from Contracts with Customers	[7]									$ 2,935

[1] Includes regulatory revenue, lease revenue, sublease rental income, which are not within the scope of ASC 606.

[2] Includes primarily VPN data networks, Ethernet, IP and other ancillary services

[3] Includes primarily broadband, private line (including business data services) and other ancillary services.

[4] Includes local voice, including wholesale voice, and other ancillary services.

[5] Includes IT services and managed services revenue.

[6] Includes CAF II and federal and state USF support revenue.

[7] Includes telecommunications and data services we bill to our affiliates.