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]
Revenues	$ 5,818	$ 4,034	$ 17,665	$ 12,333
Adjustments	(312)		(947)
Total Revenue from Contracts with Customers	5,506		16,718
Transferred at Point in Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue from Contracts with Customers	51		132
Transferred over Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue from Contracts with Customers	5,455		16,586
Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	4,285	2,425	13,033	7,485
Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	1,355	1,420	4,086	4,304
Operating segments
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	5,640	3,845	17,119	11,789
Operating segments | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	4,285	2,425	13,033	7,485
Adjustments	(71)		(217)
Total Revenue from Contracts with Customers	4,214		12,816
Operating segments | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	1,355	1,420	4,086	4,304
Adjustments	(63)		(184)
Total Revenue from Contracts with Customers	1,292		3,902
Operating segments | IP & Data Services | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	1,726	755	5,212	2,256
Adjustments	0		0
Total Revenue from Contracts with Customers	1,726		5,212
Operating segments | IP & Data Services | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	70	98	249	308
Adjustments	(9)		(25)
Total Revenue from Contracts with Customers	61		224
Operating segments | Transport & Infrastructure | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	1,331	735	4,021	2,426
Adjustments	(71)		(217)
Total Revenue from Contracts with Customers	1,260		3,804
Operating segments | Transport & Infrastructure | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	720	697	2,171	2,063
Adjustments	(54)		(159)
Total Revenue from Contracts with Customers	666		2,012
Operating segments | Voice & Collaboration | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	1,075	765	3,324	2,319
Adjustments	0		0
Total Revenue from Contracts with Customers	1,075		3,324
Operating segments | Voice & Collaboration | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	565	625	1,666	1,933
Adjustments	0		0
Total Revenue from Contracts with Customers	565		1,666
Operating segments | IT & Managed Services | Business
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	153	170	476	484
Adjustments	0		0
Total Revenue from Contracts with Customers	153		476
Corporate, Non-Segment
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	178	189	546	544
Adjustments	(178)		(546)
Total Revenue from Contracts with Customers	0		0
Corporate, Non-Segment | Regulatory Revenue
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	178	$ 189	546	$ 544
Adjustments	(178)		(546)
Total Revenue from Contracts with Customers	$ 0		$ 0