Background and Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) derivative_agreement	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Feb. 25, 2019 shares	Jan. 01, 2019 USD ($)
Finite-Lived Intangible Assets [Line Items]
Advertising expense	$ 56,000,000	$ 62,000,000	$ 98,000,000
Book overdraft balance	$ 0	106,000,000
Unissued shares of CenturyLink common stock (in shares) | shares	49,000,000
Preferred stock dividends (in dollars per share) | $ / shares	$ 25
Number of shares issued per share of common stock | shares					1
Revenues	$ 20,712,000,000	21,458,000,000	22,580,000,000
Cost of services and products	8,934,000,000	9,134,000,000	9,999,000,000
Stockholders' equity	11,162,000,000	13,470,000,000	19,828,000,000
Income tax expense	450,000,000	503,000,000	170,000,000
Right-of-use asset	1,699,000,000	1,686,000,000				$ 2,100,000,000
Operating lease liability	1,784,000,000					$ 2,200,000,000
Retained Earnings (Accumulated Deficit)
Finite-Lived Intangible Assets [Line Items]
Stockholders' equity	(8,031,000,000)	(6,814,000,000)	(1,643,000,000)	$ 1,103,000,000
Income tax expense		(2,000,000)	37,000,000
Retained Earnings (Accumulated Deficit) | Cumulative Effect, Period of Adoption, Adjustment
Finite-Lived Intangible Assets [Line Items]
Stockholders' equity		9,000,000	96,000,000
Retained Earnings (Accumulated Deficit) | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2014-09
Finite-Lived Intangible Assets [Line Items]
Stockholders' equity				338,000,000
Income tax expense				119,000,000
Retained Earnings (Accumulated Deficit) | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2018-02
Finite-Lived Intangible Assets [Line Items]
Stockholders' equity				407,000,000
Accumulated Other Comprehensive Loss
Finite-Lived Intangible Assets [Line Items]
Stockholders' equity	(2,813,000,000)	(2,680,000,000)	(2,461,000,000)	(1,995,000,000)
Accumulated Other Comprehensive Loss | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2018-02
Finite-Lived Intangible Assets [Line Items]
Stockholders' equity				$ (407,000,000)
Change in Accounting Principle, Universal Service Fund
Finite-Lived Intangible Assets [Line Items]
Revenues	(911,000,000)	(943,000,000)	(863,000,000)
Cost of services and products	$ (911,000,000)	$ (943,000,000)	$ (863,000,000)
Interest rate swaps
Finite-Lived Intangible Assets [Line Items]
Number of instruments | derivative_agreement		11
Capitalized software
Finite-Lived Intangible Assets [Line Items]
Estimated useful life	7 years
Minimum
Finite-Lived Intangible Assets [Line Items]
Contract term	1 year
Customer relationship period for revenue recognition	10 years
Minimum | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Estimated useful life	7 years
Minimum | Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Estimated useful life	4 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Contract term	5 years
Customer relationship period for revenue recognition	20 years
Maximum | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Estimated useful life	15 years
Maximum | Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Estimated useful life	20 years
Weighted Average | Consumer Customers
Finite-Lived Intangible Assets [Line Items]
Length of customer life	30 months
Weighted Average | Business Customer
Finite-Lived Intangible Assets [Line Items]
Length of customer life	30 months