Commitments and Contingencies (Details)		1 Months Ended	12 Months Ended			24 Months Ended
	Oct. 14, 2011	Feb. 28, 2017 USD ($)	Dec. 31, 2017 USD ($) lawsuit	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2007 USD ($)	Sep. 30, 2017 USD ($)
Commitments and Contingencies
Number of patents allegedly infringed, minimum			1
Capital lease activity
Assets acquired through capital leases			$ 35,000,000	$ 45,000,000	$ 17,000,000
Depreciation expense			50,000,000	70,000,000	96,000,000
Cash payments towards capital leases			48,000,000	58,000,000	89,000,000
Assets included in property, plant and equipment			342,000,000	705,000,000
Accumulated depreciation			153,000,000	351,000,000
Future annual minimum payments under capital lease arrangements
2018			56,000,000
2019			45,000,000
2020			32,000,000
2021			25,000,000
2022			22,000,000
2023 and thereafter			203,000,000
Total minimum payments			383,000,000
Less: amount representing interest and executory costs			(117,000,000)
Present value of minimum payments			266,000,000
Less: current portion			(40,000,000)
Long-term portion			226,000,000
Operating Leases
Rent expense			550,000,000	482,000,000	467,000,000
Sublease rental income			13,000,000	$ 12,000,000	$ 12,000,000
Future rental commitments
2018			666,000,000
2019			533,000,000
2020			467,000,000
2021			367,000,000
2022			326,000,000
2023 and thereafter			2,116,000,000
Total future minimum payments			4,475,000,000
Minimum sublease rentals due in the future under non-cancelable subleases			92,000,000
Purchase obligations maturities
Total purchase commitments			953,000,000
2017			343,000,000
2018 and 2019			265,000,000
2020 and 2021			103,000,000
2022 and thereafter			242,000,000
Unfavorable regulatory action
Commitments and Contingencies
Reasonable expectation of loss, maximum per proceeding			$ 100,000
William Douglas Fulghum, et al. v. Embarq Corporation
Commitments and Contingencies
Effect of modifications made to Embarq's benefits program, greater than						$ 300,000,000
Abbott et al. v. Sprint Nextel et al.
Commitments and Contingencies
Number of plaintiffs have alleged breach of fiduciary duty (plaintiffs)	1,500
CenturyLink, Inc. | Interexchange Carriers
Commitments and Contingencies
Loss contingency, pending claims, number | lawsuit			100
Level 3 Parent, LLC
Commitments and Contingencies
Loss contingency, damages sought, value			$ 50,000,000
Level 3 Parent, LLC | Loss from catastrophes
Commitments and Contingencies
Reasonable expectation of loss, maximum per proceeding							$ 6,000,000
Judicial ruling | Missouri Municipalities
Commitments and Contingencies
Pending cases, final order		1
Litigation settlement, amount awarded to other party		$ 4,000,000
Peruvian Tax Litigation | Pending litigation | Level 3 Parent, LLC
Commitments and Contingencies
Loss contingency, asserted claim			15,000,000
Peruvian Tax Litigation, Before Interest | Pending litigation | Level 3 Parent, LLC
Commitments and Contingencies
Loss contingency, asserted claim			26,000,000
Peruvian Tax Litigation, Income Taxwitholding 2001 and 2002 | Pending litigation | Level 3 Parent, LLC
Commitments and Contingencies
Loss contingency, asserted claim			3,000,000
Peruvian Tax Litigation, Vat for 2001 and 2002 | Pending litigation | Level 3 Parent, LLC
Commitments and Contingencies
Loss contingency, asserted claim			7,000,000
Peruvian Tax Litigation, Disallowance of VAT 2005 | Pending litigation | Level 3 Parent, LLC
Commitments and Contingencies
Loss contingency, asserted claim			16,000,000
Employee Severance and Contractor Termination Disputes | Pending litigation | Level 3 Parent, LLC
Commitments and Contingencies
Loss contingency, asserted claim			17,000,000
Maximum | Loss from catastrophes
Commitments and Contingencies
Reasonable expectation of loss, maximum per proceeding							25,000,000
Maximum | Brazilian Tax Claims | Pending litigation | Level 3 Parent, LLC
Commitments and Contingencies
Loss contingency, range of possible loss, portion not accrued			$ 53,000,000
Minimum | Loss from catastrophes
Commitments and Contingencies
Reasonable expectation of loss, maximum per proceeding							$ 20,000,000