Long-Term Debt and Credit Facilities (Details 2) $ in Millions												12 Months Ended
	Jan. 29, 2018 USD ($)	Nov. 02, 2017	Jun. 19, 2017 USD ($)	May 05, 2017 USD ($)	Apr. 28, 2017 USD ($)	Sep. 15, 2016 USD ($)	Aug. 29, 2016 USD ($)	Aug. 22, 2016 USD ($)	Apr. 06, 2016 USD ($)	Jan. 29, 2016 USD ($)	Feb. 20, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jan. 21, 2018 USD ($)	Nov. 01, 2017 USD ($)	Aug. 01, 2017 USD ($)	Jul. 19, 2017	Jun. 15, 2017 USD ($)	May 08, 2017 USD ($)	May 04, 2017 USD ($)	Apr. 03, 2017 USD ($)	Dec. 23, 2016 USD ($)	Sep. 19, 2016 USD ($)	Jun. 01, 2016 USD ($)	May 02, 2016 USD ($)	Apr. 30, 2011 USD ($)
Long-term Debt and Credit Facilities
Net loss on early retirement of debt												$ 5.0	$ 27.0	$ 0.0
Total long-term debt												37,554.0
Interest expense:
Gross interest expense												1,559.0	1,372.0	1,364.0
Capitalized interest												(78.0)	(54.0)	(52.0)
Total interest expense												$ 1,481.0	1,318.0	$ 1,312.0
Long-term debt, gross
Long-term Debt and Credit Facilities
Total long-term debt			$ 9,945.0
Level 3 Parent, LLC
Long-term Debt and Credit Facilities
Business Combination, Excess Fair Value of Senior Debt Over Stated Principal																$ 190.0
Revolving credit facility | CenturyLink, Inc. | 2017 revolving credit facility | Subsequent event
Long-term Debt and Credit Facilities
Maximum borrowing capacity	$ 2,168.0
Revolving credit facility | CenturyLink Escrow, LLC | 2017 revolving credit facility
Long-term Debt and Credit Facilities
Maximum borrowing capacity			$ 2,000.0
Lenders of Credit Facility			18
Total long-term debt																400.0
Revolving credit facility | CenturyLink Escrow, LLC | 2017 revolving credit facility | Minimum
Long-term Debt and Credit Facilities
Lending commitment per lender			$ 36.4
Revolving credit facility | CenturyLink Escrow, LLC | 2017 revolving credit facility | Minimum | London Interbank Offered Rate (LIBOR)
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)			2.25%
Revolving credit facility | CenturyLink Escrow, LLC | 2017 revolving credit facility | Minimum | Base Rate
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)			1.25%
Revolving credit facility | CenturyLink Escrow, LLC | 2017 revolving credit facility | Maximum
Long-term Debt and Credit Facilities
Lending commitment per lender			$ 167.8
Revolving credit facility | CenturyLink Escrow, LLC | 2017 revolving credit facility | Maximum | London Interbank Offered Rate (LIBOR)
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)			3.00%
Revolving credit facility | CenturyLink Escrow, LLC | 2017 revolving credit facility | Maximum | Base Rate
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)			2.00%
Revolving credit facility | CenturyLink Escrow, LLC | 2017 revolving credit facility | Swingline loan
Long-term Debt and Credit Facilities
Maximum borrowing capacity			$ 100.0
Revolving credit facility | CenturyLink Escrow, LLC | 2017 revolving credit facility | Letter of credit
Long-term Debt and Credit Facilities
Maximum borrowing capacity			400.0
Medium-term notes | Qwest Corporation
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												3.57%
Total long-term debt												$ 100.0	100.0
Medium-term notes | Qwest Corporation | Term loan
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance											$ 100.0
Total long-term debt												$ 100.0	100.0
Medium-term notes | Qwest Corporation | Term loan | Minimum | London Interbank Offered Rate (LIBOR)
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)											1.50%
Medium-term notes | Qwest Corporation | Term loan | Minimum | Base Rate
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)											0.50%
Medium-term notes | Qwest Corporation | Term loan | Maximum | London Interbank Offered Rate (LIBOR)
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)											2.50%
Medium-term notes | Qwest Corporation | Term loan | Maximum | Base Rate
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)											1.50%
Medium-term notes | CenturyLink, Inc.
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												0.00%
Total long-term debt												$ 0.0	336.0
Medium-term notes | CenturyLink, Inc. | Subsequent event
Long-term Debt and Credit Facilities
Net proceeds from issuance of debt	132.0
Medium-term notes | CenturyLink, Inc. | Term Loan A
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												4.319%
Total long-term debt												$ 1,575.0	0.0
Medium-term notes | CenturyLink, Inc. | Term Loan A | Subsequent event
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance	$ 1,707.0
Medium-term notes | CenturyLink, Inc. | Term Loan A-1
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												4.319%
Total long-term debt												$ 370.0	0.0
Medium-term notes | CenturyLink, Inc. | Term Loan B
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												4.319%
Total long-term debt												$ 6,000.0	0.0
Medium-term notes | CenturyLink Escrow, LLC
Long-term Debt and Credit Facilities
Total long-term debt																7,945.0
Medium-term notes | CenturyLink Escrow, LLC | Term Loan A
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance			$ 1,575.0
Lenders of Credit Facility			17
Medium-term notes | CenturyLink Escrow, LLC | Term Loan A | Minimum
Long-term Debt and Credit Facilities
Lending commitment per lender			$ 28.6
Medium-term notes | CenturyLink Escrow, LLC | Term Loan A | Minimum | London Interbank Offered Rate (LIBOR)
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)			2.25%
Medium-term notes | CenturyLink Escrow, LLC | Term Loan A | Minimum | Base Rate
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)			1.25%
Medium-term notes | CenturyLink Escrow, LLC | Term Loan A | Maximum
Long-term Debt and Credit Facilities
Lending commitment per lender			$ 132.2
Medium-term notes | CenturyLink Escrow, LLC | Term Loan A | Maximum | London Interbank Offered Rate (LIBOR)
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)			3.00%
Medium-term notes | CenturyLink Escrow, LLC | Term Loan A | Maximum | Base Rate
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)			2.00%
Medium-term notes | CenturyLink Escrow, LLC | Term Loan A-1
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance			$ 370.0
Medium-term notes | CenturyLink Escrow, LLC | Term Loan A-1 | Minimum | London Interbank Offered Rate (LIBOR)
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)			2.25%
Medium-term notes | CenturyLink Escrow, LLC | Term Loan A-1 | Minimum | Base Rate
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)			1.25%
Medium-term notes | CenturyLink Escrow, LLC | Term Loan A-1 | Maximum | London Interbank Offered Rate (LIBOR)
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)			3.00%
Medium-term notes | CenturyLink Escrow, LLC | Term Loan A-1 | Maximum | Base Rate
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)			2.00%
Medium-term notes | CenturyLink Escrow, LLC | Term Loan B
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance			$ 6,000.0
Interest rate, stated percentage (as a percent)			1.375%															2.75%
Medium-term notes | CenturyLink Escrow, LLC | Term Loan B | London Interbank Offered Rate (LIBOR)
Long-term Debt and Credit Facilities
Interest rate margin (as a percent)		2.75%
Medium-term notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												3.696%
Total long-term debt												$ 4,611.0	0.0
Medium-term notes | Level 3 Financing, Inc. | Term loan
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												1.25%
Senior notes | Qwest Corporation
Long-term Debt and Credit Facilities
Total long-term debt												$ 7,294.0	7,259.0
Senior notes | Qwest Corporation | Minimum
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												6.125%
Senior notes | Qwest Corporation | Maximum
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												7.75%
Senior notes | Qwest Corporation | 6.75% Notes due 2057
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance					$ 575.0
Interest rate, stated percentage (as a percent)					6.75%
Principal amount of over-allotment					$ 85.0
Net proceeds from issuance of debt				$ 638.0
Senior notes | Qwest Corporation | 6.5% Notes due 2056
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance								$ 978.0
Interest rate, stated percentage (as a percent)								6.50%
Principal amount of over-allotment								$ 128.0
Net proceeds from issuance of debt								$ 946.0
Senior notes | Qwest Corporation | 7.00% Notes due 2056
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance										$ 235.0
Interest rate, stated percentage (as a percent)										7.00%
Net proceeds from issuance of debt										$ 227.0
Senior notes | Qwest Corporation | 6.5% Notes due 2017
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)																					6.50%
Repurchased face amount of Senior Notes																					$ 500.0
Senior notes | Qwest Corporation | 7.5% Notes due 2051
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance																				$ 288.0
Interest rate, stated percentage (as a percent)						7.50%														7.50%
Net loss on early retirement of debt						$ (9.0)
Repurchased face amount of Senior Notes						$ 287.0														$ 125.0
Senior notes | Qwest Corporation | 7.375% Notes Due 2051
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)							7.375%
Net loss on early retirement of debt							$ (18.0)
Repurchased face amount of Senior Notes							$ 661.0
Senior notes | Qwest Corporation | 8.375% Notes due 2016
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)																										8.375%
Repurchased face amount of Senior Notes																										$ 235.0
Senior notes | CenturyLink, Inc.
Long-term Debt and Credit Facilities
Total long-term debt												$ 8,125.0	8,975.0
Senior notes | CenturyLink, Inc. | Minimum
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												5.625%
Senior notes | CenturyLink, Inc. | Maximum
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												7.65%
Senior notes | CenturyLink, Inc. | 2017 revolving credit facility
Long-term Debt and Credit Facilities
Repurchased face amount of Senior Notes																$ 319.0
Senior notes | CenturyLink, Inc. | 7.5% Notes due 2024
Long-term Debt and Credit Facilities
Aggregate principal amount of debt issuance									$ 1,000.0
Interest rate, stated percentage (as a percent)									7.50%
Net proceeds from issuance of debt									$ 988.0
Senior notes | CenturyLink, Inc. | 5.15% Notes due 2017
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)																			5.15%
Repurchased face amount of Senior Notes																			$ 350.0
Senior notes | CenturyLink, Inc. | 6.00% Noted due 2017
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)																						6.00%
Repurchased face amount of Senior Notes																						$ 500.0
Senior notes | Embarq Corporation
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												7.995%
Total long-term debt												$ 1,485.0	1,485.0
Senior notes | Embarq Corporation | 8.77% Notes due 2017
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)																	8.77%
Repurchased face amount of Senior Notes																	$ 72.0
Senior notes | Embarq Corporation | 7.082% Notes due 2016
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)																									7.082%
Repurchased face amount of Senior Notes																									$ 1,184.0
Senior notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Total long-term debt												$ 5,315.0	0.0
Senior notes | Level 3 Financing, Inc. | Minimum
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												5.125%
Senior notes | Level 3 Financing, Inc. | Maximum
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												6.125%
Senior notes | Level 3 Parent, LLC
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												5.75%
Total long-term debt												$ 600.0	0.0
Senior notes | Level 3 Parent, LLC | Minimum
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)																5.125%
Senior notes | Level 3 Parent, LLC | Maximum
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)																6.125%
First mortgage bonds | Embarq Corporation
Long-term Debt and Credit Facilities
Total long-term debt												$ 151.0	223.0
First mortgage bonds | Embarq Corporation | Minimum
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												7.125%
First mortgage bonds | Embarq Corporation | Maximum
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												8.77%
First mortgage bonds | Embarq Corporation | 8.375% Notes due 2025
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)																							8.375%
Repurchased face amount of Senior Notes																							$ 5.0
First mortgage bonds | Embarq Corporation | 8.77% Notes due 2017
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)																								8.77%
Repurchased face amount of Senior Notes																								$ 4.0
First mortgage bonds | Embarq Corporation | 8.77% Notes due 2017 | Subsequent event
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)															8.77%
Repurchased face amount of Senior Notes															$ 13.0
Line of credit | CenturyLink, Inc.
Long-term Debt and Credit Facilities
Total long-term debt												$ 0.0	370.0
Line of credit | CenturyLink, Inc. | Minimum
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												4.153%
Line of credit | CenturyLink, Inc. | Maximum
Long-term Debt and Credit Facilities
Interest rate, stated percentage (as a percent)												4.285%
Line of credit | CenturyLink, Inc. | 2017 revolving credit facility
Long-term Debt and Credit Facilities
Total long-term debt												$ 405.0	0.0
Letter of credit | CenturyLink, Inc. | Uncommitted revolving letter of credit facility | Letter of credit
Long-term Debt and Credit Facilities
Maximum borrowing capacity																$ 225.0											$ 160.0
Letters of credit outstanding												104.0	105.0
Letter of credit | Level 3 Parent, LLC | Letter of credit
Long-term Debt and Credit Facilities
Letters of credit outstanding												36.0
Letter of credit | Level 3 Parent, LLC | Collateralized debt obligations | Letter of credit
Long-term Debt and Credit Facilities
Letters of credit outstanding												$ 30.0
Debt instrument, redemption, period one | Senior notes | Qwest Corporation | 6.75% Notes due 2057
Long-term Debt and Credit Facilities
Debt instrument, redemption, description					redeemed by Qwest Corporation, in whole or in part, on or after June 15, 2022, at a redemption price equal to 100% of the principal amount
Debt instrument, redemption, period one | Senior notes | Qwest Corporation | 6.5% Notes due 2056
Long-term Debt and Credit Facilities
Debt instrument, redemption, description								on or after September 1, 2021, at a redemption price equal to 100% of the principal amount redeemed
Debt instrument, redemption, period one | Senior notes | Qwest Corporation | 7.00% Notes due 2056
Long-term Debt and Credit Facilities
Debt instrument, redemption, description										on or after February 1, 2021, at a redemption price equal to 100% of the principal amount redeemed
Debt instrument, redemption, period one | Senior notes | CenturyLink, Inc.
Long-term Debt and Credit Facilities
Debt instrument, redemption, description												Under certain circumstances in connection with a “change of control” of CenturyLink, Inc., it will be required to make an offer to repurchase each series of these senior notes (other than two of its older series of notes) at a price of 101% of the principal amount redeemed, plus accrued and unpaid interest
Debt instrument, redemption, period one | Senior notes | CenturyLink, Inc. | 7.5% Notes due 2024
Long-term Debt and Credit Facilities
Debt instrument, redemption, description									on or after January 1, 2024, at a redemption price equal to 100% of the principal amount redeemed
Debt instrument, redemption, period one | Senior notes | Level 3 Financing, Inc.
Long-term Debt and Credit Facilities
Debt instrument, redemption, description												Also, under certain circumstances in connection with a "change of control" of Level 3 Parent, LLC, it, as well as Level 3 Financing, Inc., will be required to make an offer to repurchase each series of its outstanding senior notes at a price of 101% of the principal amount redeemed, plus accrued and unpaid interest
Debt instrument, redemption, period one | Senior notes | Level 3 Parent, LLC
Long-term Debt and Credit Facilities
Debt instrument, redemption, description												Also, under certain circumstances in connection with a "change of control" of Level 3 Parent, LLC, it, as well as Level 3 Financing, Inc., will be required to make an offer to repurchase each series of its outstanding senior notes at a price of 101% of the principal amount redeemed, plus accrued and unpaid interest
Fair value measurements determined on a nonrecurring basis | Level 2 | Fair value amount
Long-term Debt and Credit Facilities
Senior long-term debt fair value												$ 36,402.0	$ 19,639.0
Fair value measurements determined on a nonrecurring basis | Level 2 | Fair value amount | Level 3 Parent, LLC
Long-term Debt and Credit Facilities
Senior long-term debt fair value																10,716.0
Level 3 Parent, LLC | CenturyLink, Inc.
Long-term Debt and Credit Facilities
Note payable - related party																$ 1,825.0