Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Total Revenues	$ 2,010		$ 6,149
Adjustments	(72)		(221)
Total revenue from contracts with customers	1,938		5,928
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0		0
Transferred over Time
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,938		5,928
IP & Data Services
Disaggregation of Revenue [Line Items]
Total Revenues	969		2,959
Adjustments	0		0
Total revenue from contracts with customers	969		2,959
Transport & Infrastructure
Disaggregation of Revenue [Line Items]
Total Revenues	664		2,012
Adjustments	(45)		(140)
Total revenue from contracts with customers	619		1,872
Voice & Collaboration
Disaggregation of Revenue [Line Items]
Total Revenues	349		1,093
Adjustments	0		0
Total revenue from contracts with customers	349		1,093
IT & Managed Services
Disaggregation of Revenue [Line Items]
Total Revenues	1	$ 0	3	$ 0
Adjustments	0		0
Total revenue from contracts with customers	1		3
Other
Disaggregation of Revenue [Line Items]
Total Revenues	1	$ 2	4	$ 6
Adjustments	(1)		(3)
Total revenue from contracts with customers	0		1
Affiliate Revenues
Disaggregation of Revenue [Line Items]
Total Revenues	26		78
Adjustments	(26)		(78)
Total revenue from contracts with customers	$ 0		$ 0