Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								4 Months Ended	12 Months Ended			14 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	May 02, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Operating revenues by products and services
Provisional tax benefit, amount	$ 1,100
Statutory federal income tax rate (as a percent)	35.00%									35.00%	35.00%	35.00%
Federal income tax rate after enactment of Tax Reform (percentage)	21.00%
Operating revenues	$ 5,323	$ 4,034	$ 4,090	$ 4,209	$ 4,289	$ 4,382	$ 4,398	$ 4,401		$ 17,656	$ 17,470	$ 17,900
OPERATING INCOME	524	487	367	631	405	593	647	688		2,009	2,333	2,579
Net income	$ 1,117	$ 92	$ 17	$ 163	$ 42	$ 152	$ 196	$ 236		$ 1,389	$ 626	$ 878
Basic earnings per common share (in dollars per share)	$ 1.26	$ 0.17	$ 0.03	$ 0.30	$ 0.08	$ 0.28	$ 0.36	$ 0.44		$ 2.21	$ 1.16	$ 1.58
Diluted earnings per common share (in dollars per share)	$ 1.26	$ 0.17	$ 0.03	$ 0.30	$ 0.08	$ 0.28	$ 0.36	$ 0.44		$ 2.21	$ 1.16	$ 1.58
Severance expenses					$ 164
Level 3 Communications, Inc.
Operating revenues by products and services
Total acquisition-related expenses	$ 206	$ 37	$ 18	$ 10	$ 52					$ 271	$ 52		$ 323
Colocation Business and Data Centers
Operating revenues by products and services
Depreciation and amortization				$ (50)					$ (67)
Cyxtera Technologies
Operating revenues by products and services
Gain (Loss) on asset leaseback, failed-sale-leaseback transaction			(119)							(102)
Depreciation expense on reclassified assets			$ 44							44
Operating revenues										49
Net income										$ (103)
Term Loan B
Operating revenues by products and services
Interest expense related to Term loan B	$ 20	$ 44