Acquisition of Level 3 - Aggregate Consideration (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
	Nov. 01, 2017	Sep. 30, 2018	Dec. 31, 2018	Oct. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill			$ 28,031		$ 30,475	$ 19,650
Purchase Price Adjustments
Acquired finite-lived intangible assets, weighted average useful life			11 years
Customer relationships
Purchase Price Adjustments
Acquired finite-lived intangible assets, weighted average useful life			11 years
Level 3 Parent, LLC
Business Acquisition [Line Items]
Cash, accounts receivable and other current assets				$ 3,291	3,317
Property, plant and equipment				9,468	9,311
Other noncurrent assets				998	782
Current liabilities, excluding current maturities of long-term debt				(1,493)	(1,461)
Current maturities of long-term debt				(7)	(7)
Long-term debt	$ (10,600)			(10,888)	(10,888)
Deferred revenue and other liabilities				(1,743)	(1,629)
Goodwill				11,177	10,837
Total estimated aggregate consideration				19,612	19,617
Purchase Price Adjustments
Cash, accounts receivable and other current assets		$ (26)
Property, plant and equipment		157
Other noncurrent assets		216
Current liabilities, excluding current maturities of long-term debt		(32)
Current maturities of long-term debt		0
Long-term debt		0
Deferred revenue and other liabilities		(114)
Goodwill		340
Total estimated aggregate consideration		(5)
Accounts receivable, contractual value	$ 884			884
Acquired finite-lived intangible assets, weighted average useful life	12 years
Level 3 Parent, LLC | Customer relationships
Business Acquisition [Line Items]
Identifiable intangible assets				8,431	8,964
Purchase Price Adjustments
Identifiable intangible assets		(533)
Level 3 Parent, LLC | Other intangible assets
Business Acquisition [Line Items]
Identifiable intangible assets				$ 378	$ 391
Purchase Price Adjustments
Identifiable intangible assets		$ (13)