Acquisition of Level 3 (Details) - USD ($) $ / shares in Units, shares in Millions			2 Months Ended	3 Months Ended					12 Months Ended			14 Months Ended
	Nov. 02, 2017	Nov. 01, 2017	Dec. 31, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Oct. 31, 2017
Business acquisition
Cash paid for Converted RSUs awards									$ 5,000,000	$ 39,000,000	$ 4,000,000
Total long-term debt			$ 37,554,000,000	$ 37,554,000,000					37,554,000,000			$ 37,554,000,000
Goodwill			30,475,000,000	30,475,000,000				$ 19,650,000,000	$ 30,475,000,000	19,650,000,000	$ 20,742,000,000	30,475,000,000
Acquired finite-lived intangible assets, weighted average useful life		12 years							12 years
Level 3 Communications, Inc.
Business acquisition
Price per share of stock in business acquisition (per share)		$ 26.50
Business acquisition total consideration		$ 19,617,000,000
Total long-term debt assumed		(10,600,000,000)
Goodwill		10,837,000,000
Expected tax deductible amount of Goodwill		0
Cash, accounts receivable and other current assets		3,317,000,000
Property, plant and equipment		9,311,000,000
Other noncurrent assets		782,000,000
Current liabilities, excluding long-term debt		(1,461,000,000)
Current maturities of long-term debt		(7,000,000)
Long-term debt		(10,888,000,000)
Deferred credits and other liabilities		(1,629,000,000)
Total estimated aggregate consideration		19,617,000,000
Preliminary estimated fair value of acquired accounts receivable		866,000,000
Gross contractual amount of acquired accounts receivable		884,000,000
Estimated uncollectible amount of acquired accounts receivable		(18,000,000)
Transaction-related expenses			174,000,000	174,000,000				47,000,000	$ 174,000,000	47,000,000		174,000,000
Integration-related expenses									97,000,000	5,000,000
Total acquisition-related expenses				206,000,000	$ 37,000,000	$ 18,000,000	$ 10,000,000	52,000,000	271,000,000	52,000,000		323,000,000
Operating revenues (pro forma)									24,321,000,000	25,378,000,000
Net income (pro forma)									$ 1,632,000,000	$ 883,000,000
Basic earnings per share (pro forma)									$ 1,540,000	$ 0.84
Diluted earnings per share (pro forma)									$ 1,540,000	$ 0.84
Level 3 Communications, Inc. | Level 3 Communications, Inc.
Business acquisition
Transaction-related expenses		$ 47,000,000
Level 3 Communications, Inc. | Level 3 Parent, LLC
Business acquisition
Operating revenues contributed by Level 3 since acquisition date			1,390,000,000
Net loss contributed by Level 3 since acquisition date			144,000,000
Common Stock | Level 3 Communications, Inc.
Business acquisition
Stock per share issuable in business acquisition, Description	1.4286 shares of our common stock	1.4286 shares of CenturyLink common stock
Business acquisition, shares of common stock issued		517.3
Price of share of common stock (per share)													$ 18.99
Estimated liability for dissenting common shares		$ 60,000,000
Customer relationships
Business acquisition
Acquired finite-lived intangible assets, weighted average useful life									12 years
Customer relationships | Level 3 Communications, Inc.
Business acquisition
Customer relationships and other		8,964,000,000
Other intangible assets | Level 3 Communications, Inc.
Business acquisition
Customer relationships and other		$ 391,000,000
Restricted Stock Units (RSUs) | Common Stock | Level 3 Communications, Inc.
Business acquisition
Stock per share issuable in business acquisition, Description	each outstanding Level 3 restricted stock unit award granted on or after April 1, 2014 (other than these granted to outside directors of Level 3) was converted into a CenturyLink restricted stock unit award using a conversion ratio of 2.8386 to 1 as determined in accordance with a formula set forth in the merger agreement (the "Continuing RSU Awards")	Each outstanding Level 3 restricted stock unit award granted on or after April 1, 2014 (other than those granted to outside directors of Level 3) was converted into a CenturyLink restricted stock unit award using a conversion ratio of 2.8386 to 1 as determined in accordance with a formula set forth in the merger agreement (“the Continuing RSU Awards”)
Cash paid for Converted RSUs awards		$ 1,000,000
Consideration for Continuing RSUs awards		136,000,000
Medium-term notes | CenturyLink Escrow, LLC
Business acquisition
Total long-term debt		7,945,000,000
Medium-term notes | CenturyLink, Inc.
Business acquisition
Total long-term debt			$ 0	$ 0				$ 336,000,000	$ 0	$ 336,000,000		$ 0
2017 revolving credit facility | Revolving credit facility | CenturyLink Escrow, LLC
Business acquisition
Total long-term debt		400,000,000
Level 3 Parent, LLC | CenturyLink, Inc.
Business acquisition
Note payable - related party		$ 1,825,000,000
Common Stock | Level 3 Communications, Inc. | Level 3 Communications, Inc.
Business acquisition
Shares issued and outstanding													0.0
CenturyLink, Inc. | Level 3 Communications, Inc.
Business acquisition
CenturyLink, Inc. shareholders' ownership percentage		51.00%
Level 3 Communications, Inc. shareholder's ownership percentage		49.00%