Condensed Consolidating Financial Information - Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities			$ 1,141	$ 724
Cash Flows from Investing Activities:
Capital expenditures	$ (367)	$ (317)	(664)	(571)
(Increase) decrease in restricted cash and securities, net			11	(24)
Proceeds from sale of property, plant, and equipment and other assets			1	2
Net Cash Used in Investing Activities			(652)	(593)
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs			764	3,948
Payments on and repurchases of long-term debt and capital leases			(816)	(4,098)
Increase (decrease) due from-to affiliates, net			0	0
Net Cash Provided by (Used in) Financing Activities			(52)	(150)
Effect of Exchange Rates on Cash and Cash Equivalents			0	(12)
Net Change in Cash and Cash Equivalents			437	(31)
Cash and Cash Equivalents at Beginning of Period			854	580
Cash and Cash Equivalents at End of Period	1,291	549	1,291	549
Level 3 Communications, Inc.
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities			(18)	(21)
Cash Flows from Investing Activities:
Capital expenditures			0	0
(Increase) decrease in restricted cash and securities, net			5	(25)
Proceeds from sale of property, plant, and equipment and other assets			0	0
Net Cash Used in Investing Activities			5	(25)
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs			0	0
Payments on and repurchases of long-term debt and capital leases			0	(313)
Increase (decrease) due from-to affiliates, net			12	365
Net Cash Provided by (Used in) Financing Activities			12	52
Effect of Exchange Rates on Cash and Cash Equivalents			0	0
Net Change in Cash and Cash Equivalents			(1)	6
Cash and Cash Equivalents at Beginning of Period			12	7
Cash and Cash Equivalents at End of Period	11	13	11	13
Level 3 Financing, Inc.
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities			(225)	(339)
Cash Flows from Investing Activities:
Capital expenditures			0	0
(Increase) decrease in restricted cash and securities, net			0	0
Proceeds from sale of property, plant, and equipment and other assets			0	0
Net Cash Used in Investing Activities			0	0
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs			764	3,948
Payments on and repurchases of long-term debt and capital leases			(806)	(3,780)
Increase (decrease) due from-to affiliates, net			267	171
Net Cash Provided by (Used in) Financing Activities			225	339
Effect of Exchange Rates on Cash and Cash Equivalents			0	0
Net Change in Cash and Cash Equivalents			0	0
Cash and Cash Equivalents at Beginning of Period			6	5
Cash and Cash Equivalents at End of Period	6	5	6	5
Level 3 Communications, LLC
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities			274	(22)
Cash Flows from Investing Activities:
Capital expenditures			(333)	(188)
(Increase) decrease in restricted cash and securities, net			6	1
Proceeds from sale of property, plant, and equipment and other assets			0	0
Net Cash Used in Investing Activities			(327)	(187)
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs			0	0
Payments on and repurchases of long-term debt and capital leases			0	0
Increase (decrease) due from-to affiliates, net			528	191
Net Cash Provided by (Used in) Financing Activities			528	191
Effect of Exchange Rates on Cash and Cash Equivalents			0	0
Net Change in Cash and Cash Equivalents			475	(18)
Cash and Cash Equivalents at Beginning of Period			727	307
Cash and Cash Equivalents at End of Period	1,202	289	1,202	289
Other Non-Guarantor Subsidiaries
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities			1,110	1,106
Cash Flows from Investing Activities:
Capital expenditures			(331)	(383)
(Increase) decrease in restricted cash and securities, net			0	0
Proceeds from sale of property, plant, and equipment and other assets			1	2
Net Cash Used in Investing Activities			(330)	(381)
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs			0	0
Payments on and repurchases of long-term debt and capital leases			(10)	(5)
Increase (decrease) due from-to affiliates, net			(807)	(727)
Net Cash Provided by (Used in) Financing Activities			(817)	(732)
Effect of Exchange Rates on Cash and Cash Equivalents			0	(12)
Net Change in Cash and Cash Equivalents			(37)	(19)
Cash and Cash Equivalents at Beginning of Period			109	261
Cash and Cash Equivalents at End of Period	72	242	72	242
Eliminations
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities			0	0
Cash Flows from Investing Activities:
Capital expenditures			0	0
(Increase) decrease in restricted cash and securities, net			0	0
Proceeds from sale of property, plant, and equipment and other assets			0	0
Net Cash Used in Investing Activities			0	0
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs			0	0
Payments on and repurchases of long-term debt and capital leases			0	0
Increase (decrease) due from-to affiliates, net			0	0
Net Cash Provided by (Used in) Financing Activities			0	0
Effect of Exchange Rates on Cash and Cash Equivalents			0	0
Net Change in Cash and Cash Equivalents			0	0
Cash and Cash Equivalents at Beginning of Period			0	0
Cash and Cash Equivalents at End of Period	$ 0	$ 0	$ 0	$ 0