Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	$ 5,778	$ 5,818	$ 5,902	$ 5,945	$ 5,323	$ 4,034	$ 4,090	$ 4,209	$ 23,443	$ 17,656	$ 17,470
Adjustments									(1,538)
Total Revenue from Contracts with Customers									21,905
Transferred at Point in Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue from Contracts with Customers									230
Transferred over Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue from Contracts with Customers									21,675
Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue									17,349	11,220	10,704
Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue									5,371	5,704	6,062
Operating Segments | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue									17,349	11,220	10,704
Adjustments									(569)
Total Revenue from Contracts with Customers									16,780
Operating Segments | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue									5,371	5,704	6,062
Adjustments									(246)
Total Revenue from Contracts with Customers									5,125
Operating Segments | IP & Data Services | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue									6,971	3,682	2,957
Adjustments									0
Total Revenue from Contracts with Customers									6,971
Operating Segments | IP & Data Services | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue									308	401	461
Adjustments									(33)
Total Revenue from Contracts with Customers									275
Operating Segments | Transport & Infrastructure | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue									5,356	3,569	3,807
Adjustments									(569)
Total Revenue from Contracts with Customers									4,787
Operating Segments | Transport & Infrastructure | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue									2,892	2,776	2,776
Adjustments									(213)
Total Revenue from Contracts with Customers									2,679
Operating Segments | Voice & Collaboration | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue									4,401	3,317	3,299
Adjustments									0
Total Revenue from Contracts with Customers									4,401
Operating Segments | Voice & Collaboration | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue									2,171	2,527	2,825
Adjustments									0
Total Revenue from Contracts with Customers									2,171
Operating Segments | IT & Managed Services | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue									621	652	641
Adjustments									0
Total Revenue from Contracts with Customers									621
Corporate, Non-Segment
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue									723	732	704
Adjustments									(723)
Total Revenue from Contracts with Customers									0
Corporate, Non-Segment | Regulatory Revenue
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue									723	$ 732	$ 704
Adjustments									(723)
Total Revenue from Contracts with Customers									$ 0