Employee Benefits - Additional Information (Details) - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2019	Nov. 01, 2017	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	$ 14,800,000,000	$ 16,500,000,000	$ 16,700,000,000
Ultimate health care cost trend rate	4.50%
Return on plan assets	$ (350,000,000)	1,300,000,000
Expected return on plan assets	(686,000,000)	(668,000,000)
Difference between the actual and expected returns on pension and post-retirement plan assets	1,000,000,000	639,000,000
Active health care benefit expenses	434,000,000	341,000,000	399,000,000
Participating employees' contribution to health care plan	$ 142,000,000	$ 128,000,000	127,000,000
CenturyLink, Inc. common stock included in the assets of the Defined Contribution Plan (in shares)	12	7
Expenses related to the 401(k) Plan	$ 93,000,000	$ 77,000,000	79,000,000
Minimum
Defined Benefit Plan Disclosure [Line Items]
Remaining estimated life of plan participants	8 years
Initial health care cost trend rate	5.00%
Maximum
Defined Benefit Plan Disclosure [Line Items]
Remaining estimated life of plan participants	9 years
Initial health care cost trend rate	7.00%
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan	$ (1,561,000,000)	(2,004,000,000)
Benefit obligation	11,594,000,000	13,064,000,000	13,244,000,000			$ 13,287,000,000
Fair value of plan assets	$ 10,033,000,000	11,060,000,000	10,892,000,000			11,072,000,000
Amortization period of the plan shortfall	7 years
Employer contributions	$ 500,000,000	100,000,000	100,000,000
Benefits paid by company	0	0	0
Expected future benefits, next twelve months	966,000,000
Special termination benefits charge	$ 15,000,000	$ 0	$ 13,000,000
Expected long-term rate of return on plan assets before administrative expenses	7.00%
Expected long-term rate of return on plan assets	6.50%	6.50%	7.00%
Short term interest crediting rates	3.25%
Long term interest crediting rates	4.00%
Return on plan assets	$ (349,000,000)	$ 1,306,000,000	$ 754,000,000
Expected return on plan assets	(685,000,000)	(666,000,000)	(733,000,000)
Pension Plan | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 24,000,000	27,000,000	11,000,000
Pension Plan | Debt Security
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percentage	31.00%
Pension Plan | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percentage	29.00%
Pension Plan | High Yield Bonds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 7,000,000	7,000,000	11,000,000
Pension Plan | Domestic Equity Securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,000,000	3,000,000	0
Pension Plan | Cash and Cash Equivalents | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	1,000,000	0
Pension Plan | U.S. Stocks
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percentage	26.00%
Pension Plan | Private Equity
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percentage	14.00%
Pension Plan | Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan	$ (1,600,000,000)	(2,000,000,000)
Employer contributions	500,000,000	100,000,000
Pension Plan | Nonqualified Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan	(52,000,000)	(58,000,000)
Benefits paid by company	5,000,000	5,000,000
Expected future benefits, next twelve months	5,000,000
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan	(2,959,000,000)	(3,352,000,000)
Benefit obligation	2,977,000,000	3,375,000,000	3,413,000,000			3,567,000,000
Fair value of plan assets	18,000,000	23,000,000	53,000,000			$ 193,000,000
Employer contributions	0	0
Benefits paid by company	311,000,000	$ 298,000,000	$ 191,000,000
Expected future benefits, next twelve months	277,000,000
Benefits paid, net of participant contributions and direct subsidy receipts	249,000,000
Expected future benefit payment, next twelve months, net of direct subsidies	$ 270,000,000
Ultimate health care cost trend rate	4.50%	4.50%	4.50%
Special termination benefits charge	$ 0	$ 0	$ 3,000,000
Expected long-term rate of return on plan assets	4.00%	5.00%	7.00%
Return on plan assets	$ (1,000,000)	$ 1,000,000	$ 5,000,000
Expected return on plan assets	$ (1,000,000)	$ (2,000,000)	(7,000,000)
Other Postretirement Benefits Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate	5.00%	5.00%
Other Postretirement Benefits Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate	7.00%	7.00%
Level 3 Parent, LLC | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan	$ (11,000,000)	$ (20,000,000)			$ (20,000,000)
Benefit obligation	144,000,000	167,000,000
Fair value of plan assets	133,000,000	147,000,000
Level 3 Parent, LLC | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan					$ 1,000,000
Scenario, Forecast | Minimum
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate				5.00%
Scenario, Forecast | Maximum
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate				6.50%
Change in Assumptions for Defined Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	(38,000,000)	(113,000,000)	$ (268,000,000)
Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,108,000,000	5,441,000,000
Fair Value, Measurements, Recurring | Pension Plan | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,326,000,000	2,827,000,000
Fair Value, Measurements, Recurring | Pension Plan | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,758,000,000	2,587,000,000
Fair Value, Measurements, Recurring | Pension Plan | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24,000,000	27,000,000
Fair Value, Measurements, Recurring | Pension Plan | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,000,000	2,000,000
Fair Value, Measurements, Recurring | Pension Plan | Derivatives | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,000,000	2,000,000
Fair Value, Measurements, Recurring | Pension Plan | Derivatives | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(2,000,000)	0
Fair Value, Measurements, Recurring | Pension Plan | Derivatives | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Measurements, Recurring | Pension Plan | Investment Grade Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,851,000,000	1,747,000,000
Fair Value, Measurements, Recurring | Pension Plan | Investment Grade Bonds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	458,000,000	432,000,000
Fair Value, Measurements, Recurring | Pension Plan | Investment Grade Bonds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,393,000,000	1,315,000,000
Fair Value, Measurements, Recurring | Pension Plan | Investment Grade Bonds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Measurements, Recurring | Pension Plan | High Yield Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	284,000,000	582,000,000
Fair Value, Measurements, Recurring | Pension Plan | High Yield Bonds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Measurements, Recurring | Pension Plan | High Yield Bonds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	277,000,000	575,000,000
Fair Value, Measurements, Recurring | Pension Plan | High Yield Bonds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,000,000	7,000,000
Fair Value, Measurements, Recurring | Pension Plan | U.S. Stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	768,000,000	1,035,000,000
Fair Value, Measurements, Recurring | Pension Plan | U.S. Stocks | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	764,000,000	1,030,000,000
Fair Value, Measurements, Recurring | Pension Plan | U.S. Stocks | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,000,000	2,000,000
Fair Value, Measurements, Recurring | Pension Plan | U.S. Stocks | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,000,000	3,000,000
Fair Value, Measurements, Recurring | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1,000,000
Fair Value, Measurements, Recurring | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1,000,000
Fair Value, Measurements, Recurring | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Measurements, Recurring | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	0
Fair Value, Measurements, Recurring | Other Postretirement Benefits Plan | U.S. Stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,000,000
Fair Value, Measurements, Recurring | Other Postretirement Benefits Plan | U.S. Stocks | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,000,000
Fair Value, Measurements, Recurring | Other Postretirement Benefits Plan | U.S. Stocks | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Fair Value, Measurements, Recurring | Other Postretirement Benefits Plan | U.S. Stocks | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 0