Goodwill, Customer Relationships and Other Intangible Assets - Goodwill Activity (Details) - USD ($) $ in Millions		3 Months Ended			12 Months Ended
	Oct. 31, 2018	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill Activity
As of January 1, 2019		$ 28,031		$ 30,475	$ 28,031	$ 30,475
Goodwill acquired during period						282
Goodwill impairment	$ (2,700)	(6,500)	$ (2,700)	(2,700)	(6,506)	(2,726)	$ 0
As of December 31, 2019			28,031		21,534	28,031	30,475
Effect of foreign currency rate change and other					9	(58)
Level 3 Parent, LLC
Goodwill Activity
As of January 1, 2019				10,837		10,837
As of December 31, 2019	$ 11,177						10,837
Business
Goodwill Activity
As of January 1, 2019		20,447		20,197	20,447	20,197
Goodwill acquired during period						250
Goodwill impairment						0
As of December 31, 2019			20,447			20,447	20,197
Goodwill accumulated impairment loss							1,100
Consumer
Goodwill Activity
As of January 1, 2019		$ 7,584		$ 10,278	7,584	10,278
Goodwill acquired during period						32
Goodwill impairment					(186)	(2,726)
As of December 31, 2019			$ 7,584		7,054	7,584	$ 10,278
Effect of foreign currency rate change and other					$ 0
Consumer | Level 3 Parent, LLC
Goodwill Activity
Goodwill acquired during period						$ 32