Commitments, Contingencies and Other Items (Details)	1 Months Ended	9 Months Ended	12 Months Ended
	Feb. 28, 2017 USD ($) lawsuit	Dec. 31, 2018 USD ($) lawsuit	Dec. 31, 2018 USD ($) patent property lawsuit	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Commitments and Contingencies
Proceeds from Rents Received			$ 882,000,000	$ 766,000,000	$ 734,000,000
Litigation liability		$ 123,000,000	$ 123,000,000
Number of patents allegedly infringed, minimum | patent			1
Lease expense			$ 875,000,000	550,000,000	482,000,000
Capital lease activity
Assets acquired through capital leases			25,000,000	35,000,000	45,000,000
Depreciation expense			51,000,000	50,000,000	70,000,000
Cash payments towards capital leases			48,000,000	48,000,000	58,000,000
Assets included in property, plant and equipment		427,000,000	427,000,000	420,000,000
Accumulated depreciation		180,000,000	180,000,000	154,000,000
Future annual minimum payments under capital lease arrangements
2019		51,000,000	51,000,000
2020		36,000,000	36,000,000
2021		23,000,000	23,000,000
2022		21,000,000	21,000,000
2023		20,000,000	20,000,000
2024 and thereafter		183,000,000	183,000,000
Total minimum payments		334,000,000	334,000,000
Less: amount representing interest and executory costs		(100,000,000)	(100,000,000)
Present value of minimum payments		234,000,000	234,000,000
Less: current portion		(38,000,000)	(38,000,000)
Long-term portion		196,000,000	196,000,000
Future rental commitments
2019		832,000,000	832,000,000
2020		577,000,000	577,000,000
2021		467,000,000	467,000,000
2022		399,000,000	399,000,000
2023		356,000,000	356,000,000
2024 and thereafter		1,724,000,000	1,724,000,000
Total future minimum payments		4,355,000,000	4,355,000,000
Minimum sublease rentals due in the future under non-cancelable subleases		101,000,000	101,000,000
Purchase obligations maturities
Total purchase commitments		921,000,000	921,000,000
2019		322,000,000	322,000,000
2020 and 2021		325,000,000	325,000,000
2022 and 2023		88,000,000	88,000,000
2024 and thereafter		186,000,000	186,000,000
Operating Leases, Income Statement, Sublease Revenue			$ 21,000,000	$ 13,000,000	$ 12,000,000
Site Contingency, Number Of Properties With Potential Environmental Liability | property			200
Unfavorable regulatory action
Commitments and Contingencies
Reasonable expectation of loss, maximum per proceeding		100,000,000	$ 100,000,000
Right-of-Way Agreements
Future rental commitments
2019		157,000,000	157,000,000
2020		134,000,000	134,000,000
2021		112,000,000	112,000,000
2022		120,000,000	120,000,000
2023		115,000,000	115,000,000
2024 and thereafter		755,000,000	755,000,000
Total future minimum payments		1,393,000,000	1,393,000,000
Operating Leases
Future rental commitments
2019		675,000,000	675,000,000
2020		443,000,000	443,000,000
2021		355,000,000	355,000,000
2022		279,000,000	279,000,000
2023		241,000,000	241,000,000
2024 and thereafter		969,000,000	969,000,000
Total future minimum payments		$ 2,962,000,000	2,962,000,000
Louisiana State Court
Commitments and Contingencies
Loss Contingency, New Claims Filed, Number | lawsuit		2
Level 3 Parent, LLC
Commitments and Contingencies
Loss contingency, damages sought, value			50,000,000
Level 3 Parent, LLC | Pending litigation | Peruvian Tax Litigation, Before Interest
Commitments and Contingencies
Loss contingency, asserted claim						$ 26,000,000
Level 3 Parent, LLC | Pending litigation | Peruvian Tax Litigation
Commitments and Contingencies
Loss contingency, asserted claim		$ 11,000,000	11,000,000
Level 3 Parent, LLC | Pending litigation | Maximum | Brazilian Tax Claims
Commitments and Contingencies
Loss contingency, range of possible loss, portion not accrued		$ 37,000,000	$ 37,000,000
Interexchange Carriers | CenturyLink, Inc.
Commitments and Contingencies
Loss contingency, pending claims, number | lawsuit		100	100
Missouri Municipalities | Judicial ruling
Commitments and Contingencies
Pending cases, final order | lawsuit	1
Litigation settlement, amount awarded to other party	$ 4,000,000