Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 5,945	$ 4,209
Adjustments	(312)
Total Revenue from Contracts with Customers	5,633
Transferred at Point in Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue from Contracts with Customers	39
Transferred over Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue from Contracts with Customers	5,594
Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	4,383	2,590
Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	1,379	1,447
Operating segments
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	5,762	4,037
Operating segments | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	4,383	2,590
Adjustments	(67)
Total Revenue from Contracts with Customers	4,316
Operating segments | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	1,379	1,447
Adjustments	(62)
Total Revenue from Contracts with Customers	1,317
Operating segments | IP & Data Services | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	1,748	744
Adjustments	0
Total Revenue from Contracts with Customers	1,748
Operating segments | IP & Data Services | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	97	120
Adjustments	(9)
Total Revenue from Contracts with Customers	88
Operating segments | Transport & Infrastructure | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	1,362	906
Adjustments	(67)
Total Revenue from Contracts with Customers	1,295
Operating segments | Transport & Infrastructure | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	756	701
Adjustments	(53)
Total Revenue from Contracts with Customers	703
Operating segments | Voice & Collaboration | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	1,111	788
Adjustments	0
Total Revenue from Contracts with Customers	1,111
Operating segments | Voice & Collaboration | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	526	626
Adjustments	0
Total Revenue from Contracts with Customers	526
Operating segments | IT & Managed Services | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	162	152
Adjustments	0
Total Revenue from Contracts with Customers	162
Corporate, Non-Segment
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	183	172
Adjustments	(183)
Total Revenue from Contracts with Customers	0
Corporate, Non-Segment | Regulatory Revenue
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	183	$ 172
Adjustments	(183)
Total Revenue from Contracts with Customers	$ 0