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
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	$ 2,149	$ 2,141	$ 6,380	$ 6,436
Adjustments for non-ASC 606 revenue	(82)		(240)
Total revenues from contracts with customers	2,067		6,140
Transferred at Point in Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues from contracts with customers	13		35
Transferred over Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues from contracts with customers	2,054		6,105
IP & Data Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	155	161	460	475
Adjustments for non-ASC 606 revenue	0		0
Total revenues from contracts with customers	155		460
Transport & Infrastructure
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	739	751	2,216	2,268
Adjustments for non-ASC 606 revenue	(29)		(83)
Total revenues from contracts with customers	710		2,133
Voice & Collaboration
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	448	492	1,370	1,504
Adjustments for non-ASC 606 revenue	0		0
Total revenues from contracts with customers	448		1,370
IT & Managed Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	2	0	6	0
Adjustments for non-ASC 606 revenue	0		0
Total revenues from contracts with customers	2		6
Regulatory Revenue
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	53	52	157	159
Adjustments for non-ASC 606 revenue	(53)		(157)
Total revenues from contracts with customers	0		0
Affiliate services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	752	$ 685	2,171	$ 2,030
Adjustments for non-ASC 606 revenue	0		0
Total revenues from contracts with customers	$ 752		$ 2,171