Employee Benefits - Additional Information (Details) - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Nov. 01, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	$ 15,300,000,000	$ 14,800,000,000	$ 16,500,000,000
Expected future benefits, next twelve months	5,000,000
Benefits paid, net of participant contributions and direct subsidy receipts	245,000,000
Expected future benefit payment, next twelve months, net of direct subsidies	$ 236,000,000
Increase (decrease) in plan participants	(3.00%)
Ultimate health care cost trend rate	4.50%
Commingled funds, redemption notice	270 days
Return on plan assets	$ 1,600,000,000	(350,000,000)
Expected return on plan assets	(619,000,000)	(686,000,000)
Difference between the actual and expected returns on pension and post-retirement plan assets	1,000,000,000.0	1,000,000,000.0
Active health care benefit expenses	381,000,000	434,000,000	341,000,000
Participating employees' contribution to health care plan	$ 148,000,000	$ 142,000,000	128,000,000
CenturyLink, Inc. common stock included in the assets of the Defined Contribution Plan (in shares)	11	12
Expenses related to the 401(k) Plan	$ 113,000,000	$ 93,000,000	77,000,000
Minimum
Defined Benefit Plan Disclosure [Line Items]
Remaining estimated life of plan participants	16 years
Initial health care cost trend rate	5.00%
Maximum
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate	6.50%
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan	$ (1,724,000,000)	(1,561,000,000)
Benefit obligation	12,217,000,000	11,594,000,000	13,064,000,000		$ 13,244,000,000
Fair value of plan assets	10,493,000,000	10,033,000,000	11,060,000,000		10,892,000,000
Employer contributions	0	500,000,000	100,000,000
Expected future benefits, next twelve months	971,000,000
Special termination benefits charge	$ 6,000,000	$ 15,000,000	$ 0
Expected long-term rate of return on plan assets before administrative expenses	6.50%
Expected long-term rate of return on plan assets	6.50%	6.50%	6.50%
Short term interest crediting rates	2.25%
Long term interest crediting rates	4.00%
Return on plan assets	$ 1,575,000,000	$ (349,000,000)	$ 1,306,000,000
Expected return on plan assets	(618,000,000)	(685,000,000)	(666,000,000)
Pension Plan | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22,000,000	24,000,000	27,000,000
Pension Plan | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 3,864,000,000	4,925,000,000
Pension Plan | Defined Benefit Plan, Debt Security
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percentage	50.00%
Pension Plan | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation, percentage	50.00%
Pension Plan | Investment Grade Bonds | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 211,000,000	109,000,000
Pension Plan | High Yield Bonds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,000,000	7,000,000	7,000,000
Pension Plan | High Yield Bonds | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	39,000,000	388,000,000
Pension Plan | Domestic Equity Securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,000,000	2,000,000	3,000,000
Pension Plan | Cash and Cash Equivalents | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0	1,000,000
Pension Plan | U.S. Stocks | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	169,000,000	150,000,000
Pension Plan | Private Equity | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	322,000,000	347,000,000
Pension Plan | Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan	1,700,000,000	(1,600,000,000)
Employer contributions		500,000,000
Pension Plan | Nonqualified Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan	51,000,000	(52,000,000)
Benefits paid by company	5,000,000	5,000,000
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan	(3,024,000,000)	(2,959,000,000)
Benefit obligation	3,037,000,000	2,977,000,000	3,375,000,000		3,413,000,000
Fair value of plan assets	13,000,000	18,000,000	23,000,000		$ 53,000,000
Employer contributions	0	0
Benefits paid by company	300,000,000	$ 311,000,000	$ 298,000,000
Expected future benefits, next twelve months	$ 242,000,000
Ultimate health care cost trend rate	4.50%	4.50%	4.50%
Expected long-term rate of return on plan assets	4.00%	4.00%	5.00%
Return on plan assets	$ (1,000,000)	$ (1,000,000)	$ 1,000,000
Expected return on plan assets	$ (1,000,000)	$ (1,000,000)	(2,000,000)
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	6.50%	7.00%
Other Postretirement Benefits Plan | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 13,000,000	$ 18,000,000
Other Postretirement Benefits Plan | Investment Grade Bonds | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits Plan | High Yield Bonds | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits Plan | U.S. Stocks | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefits Plan | Private Equity | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,000,000	6,000,000
Level 3 Parent, LLC | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan	(18,000,000)	(11,000,000)		$ (20,000,000)
Benefit obligation	140,000,000	144,000,000
Fair value of plan assets	$ 122,000,000	133,000,000
Amortization period of the plan shortfall	7 years
Level 3 Parent, LLC | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Funded (unfunded) status of plan				$ 1,000,000
Change in Assumptions for Defined Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	$ (4,000,000)	(38,000,000)	$ (113,000,000)
Fair Value, Measurements, Recurring | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,646,000,000	5,108,000,000
Fair Value, Measurements, Recurring | Pension Plan | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,636,000,000	2,326,000,000
Fair Value, Measurements, Recurring | Pension Plan | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,988,000,000	2,758,000,000
Fair Value, Measurements, Recurring | Pension Plan | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22,000,000	24,000,000
Fair Value, Measurements, Recurring | Pension Plan | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,864,000,000	4,925,000,000
Fair Value, Measurements, Recurring | Pension Plan | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		5,000,000
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
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)
Fair Value, Measurements, Recurring | Pension Plan | Derivatives | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Fair Value, Measurements, Recurring | Pension Plan | Investment Grade Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,025,000,000	1,851,000,000
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	828,000,000	458,000,000
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	3,197,000,000	1,393,000,000
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	237,000,000	284,000,000
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	232,000,000	277,000,000
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	5,000,000	7,000,000
Fair Value, Measurements, Recurring | Pension Plan | U.S. Stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	760,000,000	768,000,000
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	756,000,000	764,000,000
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	3,000,000	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	1,000,000	2,000,000
Fair Value, Measurements, Recurring | Other Postretirement Benefits Plan
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 1
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 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 | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 13,000,000	$ 18,000,000