Revenue Recognition - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract term				30 months
Revenues	$ 5,818	$ 4,034		$ 17,665	$ 12,333
Contract Fulfillment Costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Capitalized contract cost, net	173		$ 161	173		$ 133
Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	1,355	$ 1,420		4,086	$ 4,304
Restatement Adjustment | Contract Fulfillment Costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Capitalized contract cost, net						$ 45
Accounting Standards Update 2014-09 | Impact of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	(14)			12
Costs and expenses (less than)	$ 3			$ 3
Accounting Standards Update 2014-09 | Impact of ASC 606 | Contract Fulfillment Costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Capitalized contract cost, net			45
Accounting Standards Update 2014-09 | Impact of ASC 606 | Consumer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues			43
Accounting Standards Update 2014-09 | Impact of ASC 606 | Consumer | Voice & Collaboration
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues			34
Accounting Standards Update 2014-09 | Impact of ASC 606 | Consumer | Transport & Infrastructure
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues			$ 9
Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract term				1 year
Customer relationship period				10 years
Minimum | Business Customer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Length of customer life				12 months
Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract term				7 years
Customer relationship period				20 years
Maximum | Business Customer
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Length of customer life				60 months
Weighted Average | Consumer Customers
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Length of customer life				30 months