Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	2 Months Ended	3 Months Ended								10 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Oct. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	$ 1,407	$ 2,061	$ 2,064	$ 2,014	$ 2,046	$ 2,071	$ 2,010	$ 2,052	$ 2,087	$ 6,870	$ 8,185	$ 8,220
Adjustments											(893)	(299)
Total Revenue from Contracts with Customers											7,292	7,921
Transferred at Point in Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue from Contracts with Customers											0	0
Transferred over Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue from Contracts with Customers											7,292	7,921
IP and Data Services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	668									3,284	3,888	3,945
Adjustments											0	0
Total Revenue from Contracts with Customers											3,888	3,945
Transport and Infrastructure
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	464									2,272	2,662	2,701
Adjustments											(704)	(189)
Total Revenue from Contracts with Customers											1,958	2,512
Voice and Collaboration
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	258									1,308	1,443	1,464
Adjustments											0	0
Total Revenue from Contracts with Customers											1,443	1,464
Other revenue
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	1									6	12	3
Adjustments											(9)	(3)
Total Revenue from Contracts with Customers											3	0
Affiliate revenue
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total Revenue	$ 16									$ 0	180	107
Adjustments											(180)	(107)
Total Revenue from Contracts with Customers											$ 0	$ 0