Condensed Consolidating Financial Information - Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities	$ 539	$ 510
Cash Flows from Investing Activities:
Capital expenditures	(368)	(297)
(Increase) decrease in restricted cash and securities, net	0	(828)
Proceeds from sale of property, plant, and equipment and other assets	0
Net Cash Used in Investing Activities	(368)	(1,125)
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs	4,569	765
Payments on and repurchases of long-term debt and capital leases	(4,613)	(1)
Increase (decrease) due from-to affiliates, net	0	0
Net Cash (Used in) Provided by Financing Activities	(44)	764
Effect of Exchange Rates on Cash and Cash Equivalents	1	1
Net Change in Cash and Cash Equivalents	128	150
Cash and Cash Equivalents at Beginning of Period	1,819	854
Cash and Cash Equivalents at End of Period	1,947	1,004
Level 3 Communications, Inc.
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities	(16)	(17)
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
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	16	17
Net Cash (Used in) Provided by Financing Activities	16	17
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	15	12
Cash and Cash Equivalents at End of Period	15	12
Level 3 Financing, Inc.
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities	(135)	(92)
Cash Flows from Investing Activities:
Capital expenditures	0	0
(Increase) decrease in restricted cash and securities, net	0	(829)
Proceeds from sale of property, plant, and equipment and other assets	0
Net Cash Used in Investing Activities	0	(829)
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs	4,569	765
Payments on and repurchases of long-term debt and capital leases	(4,611)	0
Increase (decrease) due from-to affiliates, net	177	156
Net Cash (Used in) Provided by Financing Activities	135	921
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	6
Cash and Cash Equivalents at End of Period	0	6
Level 3 Communications, LLC
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities	109	130
Cash Flows from Investing Activities:
Capital expenditures	(233)	(159)
(Increase) decrease in restricted cash and securities, net	0	1
Proceeds from sale of property, plant, and equipment and other assets	0
Net Cash Used in Investing Activities	(233)	(158)
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	262	187
Net Cash (Used in) Provided by Financing Activities	262	187
Effect of Exchange Rates on Cash and Cash Equivalents	0	0
Net Change in Cash and Cash Equivalents	138	159
Cash and Cash Equivalents at Beginning of Period	1,700	727
Cash and Cash Equivalents at End of Period	1,838	886
Other Non-Guarantor Subsidiaries
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities	581	489
Cash Flows from Investing Activities:
Capital expenditures	(135)	(138)
(Increase) decrease in restricted cash and securities, net	0	0
Proceeds from sale of property, plant, and equipment and other assets	0
Net Cash Used in Investing Activities	(135)	(138)
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	(2)	(1)
Increase (decrease) due from-to affiliates, net	(455)	(360)
Net Cash (Used in) Provided by Financing Activities	(457)	(361)
Effect of Exchange Rates on Cash and Cash Equivalents	1	1
Net Change in Cash and Cash Equivalents	(10)	(9)
Cash and Cash Equivalents at Beginning of Period	104	109
Cash and Cash Equivalents at End of Period	94	100
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
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 (Used in) Provided by 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

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