Background and Summary of Significant Accounting Policies - Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) reporting_unit segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Statement [Line Items]
Decrease in operating revenues	$ (7,313,000,000)	$ (8,052,000,000)	$ (8,395,000,000)
Decrease in cost of services and products	(1,995,000,000)	(2,333,000,000)	(2,669,000,000)
Advertising expense	25,000,000	28,000,000	58,000,000
Bank overdrafts	$ 0	0
Threshold for determining accounts receivable as past due, days outstanding	30 days
Number of reporting units | reporting_unit	1
Number of operating segments | segment	1
Customer relationships
Statement [Line Items]
Finite-lived intangible assets, maximum useful life	10 years
Capitalized software
Statement [Line Items]
Finite-lived intangible assets, maximum useful life	7 years
Qwest Communications International, Inc. | Pension, Supplemental and Other Postretirement Benefit Plans
Statement [Line Items]
Pension settlement term	30 years
Repayments on affiliate obligation	$ 71,000,000	76,000,000
Qwest Communications International, Inc. | Pension, Supplemental and Other Postretirement Benefit Plans
Statement [Line Items]
Repayments on affiliate obligation	$ 71,000,000	76,000,000
Minimum
Statement [Line Items]
Contract term	1 year
Customer relationship period for revenue recognition	10 years
Maximum
Statement [Line Items]
Contract term	5 years
Customer relationship period for revenue recognition	20 years
Average | Consumer customers, average contract life
Statement [Line Items]
Customer life	30 months
Average | Business customer, average contract life
Statement [Line Items]
Customer life	29 months
Change In Accounting Principle, Universal Service Fund [Member]
Statement [Line Items]
Decrease in operating revenues	$ 105,000,000	105,000,000	98,000,000
Decrease in cost of services and products	$ 105,000,000	$ 105,000,000	$ 98,000,000