Revenue Recognition - Disaggregation of revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total operating revenue	$ 2,012	$ 2,039	$ 2,051	$ 2,055	$ 2,113	$ 2,149	$ 2,101	$ 2,130	$ 8,157	$ 8,493	$ 8,550
Total revenue									7,660	7,962
Goods and services transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue									54	69
Services performed over time
Disaggregation of Revenue [Line Items]
Total revenue									7,606	7,893
IP and Data Services
Disaggregation of Revenue [Line Items]
Total operating revenue									624	615	634
Transport and Infrastructure
Disaggregation of Revenue [Line Items]
Total operating revenue									2,829	2,925	3,006
Voice and Collaboration
Disaggregation of Revenue [Line Items]
Total operating revenue									1,639	1,798	1,980
IT and Managed Services
Disaggregation of Revenue [Line Items]
Total operating revenue									3	6	0
Regulatory Services
Disaggregation of Revenue [Line Items]
Total operating revenue									189	214	211
Affiliate Services
Disaggregation of Revenue [Line Items]
Total operating revenue									2,873	2,935	$ 2,719
ASC 605 Historical Adjusted Amount
Disaggregation of Revenue [Line Items]
Total operating revenue										8,499
Total revenue									7,660	7,962
ASC 605 Historical Adjusted Amount | IP and Data Services
Disaggregation of Revenue [Line Items]
Total revenue									624	615
ASC 605 Historical Adjusted Amount | Transport and Infrastructure
Disaggregation of Revenue [Line Items]
Total revenue									2,521	2,608
ASC 605 Historical Adjusted Amount | Voice and Collaboration
Disaggregation of Revenue [Line Items]
Total revenue									1,639	1,798
ASC 605 Historical Adjusted Amount | IT and Managed Services
Disaggregation of Revenue [Line Items]
Total revenue									3	6
ASC 605 Historical Adjusted Amount | Regulatory Services
Disaggregation of Revenue [Line Items]
Total revenue									0	0
ASC 605 Historical Adjusted Amount | Affiliate Services
Disaggregation of Revenue [Line Items]
Total revenue									2,873	2,935
Accounting Standards Update 2014-09 | Impact of ASC 606
Disaggregation of Revenue [Line Items]
Total operating revenue										6
Adjustments for Non-ASC 606 Revenue									(497)	(531)
Accounting Standards Update 2014-09 | Impact of ASC 606 | IP and Data Services
Disaggregation of Revenue [Line Items]
Adjustments for Non-ASC 606 Revenue									0	0
Accounting Standards Update 2014-09 | Impact of ASC 606 | Transport and Infrastructure
Disaggregation of Revenue [Line Items]
Adjustments for Non-ASC 606 Revenue									(308)	(317)
Accounting Standards Update 2014-09 | Impact of ASC 606 | Voice and Collaboration
Disaggregation of Revenue [Line Items]
Adjustments for Non-ASC 606 Revenue									0	0
Accounting Standards Update 2014-09 | Impact of ASC 606 | IT and Managed Services
Disaggregation of Revenue [Line Items]
Adjustments for Non-ASC 606 Revenue									0	0
Accounting Standards Update 2014-09 | Impact of ASC 606 | Regulatory Services
Disaggregation of Revenue [Line Items]
Adjustments for Non-ASC 606 Revenue									(189)	(214)
Accounting Standards Update 2014-09 | Impact of ASC 606 | Affiliate Services
Disaggregation of Revenue [Line Items]
Adjustments for Non-ASC 606 Revenue									$ 0	$ 0