Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	$ 2,101	$ 2,133	$ 4,231	$ 4,295
Adjustments for non-ASC 606 revenue	(80)		(157)
Total revenues from contracts with customers	2,021		4,074
Transferred at Point in Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues from contracts with customers	11		22
Transferred over Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues from contracts with customers	2,010		4,052
IP & Data Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	154	155	305	314
Adjustments for non-ASC 606 revenue	0		0
Total revenues from contracts with customers	154		305
Transport & Infrastructure
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	732	757	1,477	1,517
Adjustments for non-ASC 606 revenue	(28)		(53)
Total revenues from contracts with customers	704		1,424
Voice & Collaboration
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	453	499	922	1,012
Adjustments for non-ASC 606 revenue	0		0
Total revenues from contracts with customers	453		922
IT & Managed Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	2	0	4	0
Adjustments for non-ASC 606 revenue	0		0
Total revenues from contracts with customers	2		4
Regulatory Revenue
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	52	53	104	107
Adjustments for non-ASC 606 revenue	(52)		(104)
Total revenues from contracts with customers	0		0
Affiliate services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	708	$ 669	1,419	$ 1,345
Adjustments for non-ASC 606 revenue	0		0
Total revenues from contracts with customers	$ 708		$ 1,419