Background and Summary of Significant Accounting Policies - Additional Information (Details) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended			12 Months Ended
	Oct. 31, 2018 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Feb. 25, 2019	Jan. 01, 2019 USD ($)
Finite-Lived Intangible Assets [Line Items]
Advertising expense					$ 62	$ 98	$ 218
Accounts receivable, past due threshold					30 days
Unissued shares of CenturyLink common stock (in shares) | shares					17
Preferred stock dividends (in dollars per share) | $ / shares					$ 25
Number of shares issued per share of common stock								1
Right-of-use asset					$ 1,686
Operating lease liability					1,758
Retained earnings			$ (1,643)		(6,814)	(1,643)
Accumulated other comprehensive loss			2,461		2,680	2,461
Goodwill impairment	$ 2,700	$ 6,500	2,700	$ 2,700	$ 6,506	2,726	$ 0
Minimum
Finite-Lived Intangible Assets [Line Items]
Contract term					1 year
Customer relationship period for revenue recognition					10 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Contract term					5 years
Customer relationship period for revenue recognition					20 years
Customer relationships | Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated useful life					7 years
Customer relationships | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated useful life					15 years
Capitalized software
Finite-Lived Intangible Assets [Line Items]
Estimated useful life					7 years
Other intangible assets | Minimum
Finite-Lived Intangible Assets [Line Items]
Estimated useful life					4 years
Other intangible assets | Maximum
Finite-Lived Intangible Assets [Line Items]
Estimated useful life					20 years
Accounting Standards Update 2016-02
Finite-Lived Intangible Assets [Line Items]
Right-of-use asset									$ 2,100
Operating lease liability									2,200
Retained earnings				407
Accumulated other comprehensive loss				$ 407
Retained Earnings | Accounting Standards Update 2014-09
Finite-Lived Intangible Assets [Line Items]
Cumulative effect of adoption of ASU			338			338
Cumulative net effect of adoption of ASU, tax			$ (119)		$ 119	$ (119)
Retained Earnings | Accounting Standards Update 2016-02
Finite-Lived Intangible Assets [Line Items]
Cumulative effect of adoption of ASU					96				$ 96
Cumulative net effect of adoption of ASU, tax					$ (37)
Consumer Customers | Weighted Average
Finite-Lived Intangible Assets [Line Items]
Length of customer life					30 months
Business Customer
Finite-Lived Intangible Assets [Line Items]
Length of customer life					49 months
Business Customer | Minimum
Finite-Lived Intangible Assets [Line Items]
Length of customer life					12 months
Business Customer | Maximum
Finite-Lived Intangible Assets [Line Items]
Length of customer life					60 months