Condensed Consolidating Financial Information - Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities		$ 1,855	$ 1,161	$ 713
Cash Flows from Investing Activities:
Capital expenditures		(1,229)	(910)	(760)
Cash related to deconsolidated Venezuela operations	$ (83)	(83)	0	0
Increase (Decrease) in Restricted Cash and Investments		(22)	(10)	13
Proceeds from sale of property, plant and equipment and other assets		4	3	0
Payments to Acquire Businesses, Net of Cash Acquired		0	(167)	0
Other		(14)	(2)	2
Net Cash Used in Investing Activities		(1,344)	(1,086)	(745)
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs		4,832	589	1,502
Payments on and repurchases of long-term debt, including current portions and refinancing costs		(5,051)	(671)	(1,796)
Increase (decrease) due from affiliates, net		0	0	0
Net Cash Provided by (Used in) Financing Activities		(219)	(82)	(294)
Effect of Exchange Rates on Cash and Cash Equivalents		(18)	(44)	(22)
Net Change in Cash and Cash Equivalents		274	(51)	(348)
Cash and Cash Equivalents at Beginning of Year		580	631	979
Cash and Cash Equivalents at End of Year		854	580	631
Level 3 Communications, Inc.
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities		(40)	(178)	(169)
Cash Flows from Investing Activities:
Capital expenditures		0	0	0
Cash related to deconsolidated Venezuela operations		0
Increase (Decrease) in Restricted Cash and Investments		(25)	0	9
Proceeds from sale of property, plant and equipment and other assets		0	0
Payments to Acquire Businesses, Net of Cash Acquired			(474)
Other		0	0	0
Net Cash Used in Investing Activities		(25)	(474)	9
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs		0	590	0
Payments on and repurchases of long-term debt, including current portions and refinancing costs		(313)	(647)	(173)
Increase (decrease) due from affiliates, net		383	708	88
Net Cash Provided by (Used in) Financing Activities		70	651	(85)
Effect of Exchange Rates on Cash and Cash Equivalents		0	0	0
Net Change in Cash and Cash Equivalents		5	(1)	(245)
Cash and Cash Equivalents at Beginning of Year		7	8
Cash and Cash Equivalents at End of Year		12	7	8
Level 3 Financing, Inc.
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities		(617)	(458)	(557)
Cash Flows from Investing Activities:
Capital expenditures		0	0	0
Cash related to deconsolidated Venezuela operations		0
Increase (Decrease) in Restricted Cash and Investments		0	0	0
Proceeds from sale of property, plant and equipment and other assets		0	0
Payments to Acquire Businesses, Net of Cash Acquired			0
Other		0	0	0
Net Cash Used in Investing Activities		0	0	0
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs		4,832	0	1,502
Payments on and repurchases of long-term debt, including current portions and refinancing costs		(4,725)	0	(1,586)
Increase (decrease) due from affiliates, net		511	457	642
Net Cash Provided by (Used in) Financing Activities		618	457	558
Effect of Exchange Rates on Cash and Cash Equivalents		0	0	0
Net Change in Cash and Cash Equivalents		1	(1)	1
Cash and Cash Equivalents at Beginning of Year		5	6
Cash and Cash Equivalents at End of Year		6	5	6
Level 3 Communications, LLC
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities		193	625	710
Cash Flows from Investing Activities:
Capital expenditures		(453)	(362)	(312)
Cash related to deconsolidated Venezuela operations		0
Increase (Decrease) in Restricted Cash and Investments		3	2	(1)
Proceeds from sale of property, plant and equipment and other assets		0	0
Payments to Acquire Businesses, Net of Cash Acquired			0
Other		(14)	0	1
Net Cash Used in Investing Activities		(464)	(360)	(312)
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs		0	0	0
Payments on and repurchases of long-term debt, including current portions and refinancing costs		(2)	0	(4)
Increase (decrease) due from affiliates, net		693	(305)	(433)
Net Cash Provided by (Used in) Financing Activities		691	(305)	(437)
Effect of Exchange Rates on Cash and Cash Equivalents		0	0	0
Net Change in Cash and Cash Equivalents		420	(40)	(39)
Cash and Cash Equivalents at Beginning of Year		307	347
Cash and Cash Equivalents at End of Year		727	307	347
Other Non-Guarantor Subsidiaries
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities		2,319	1,172	729
Cash Flows from Investing Activities:
Capital expenditures		(776)	(548)	(448)
Cash related to deconsolidated Venezuela operations		(83)
Increase (Decrease) in Restricted Cash and Investments		0	(12)	5
Proceeds from sale of property, plant and equipment and other assets		4	3
Payments to Acquire Businesses, Net of Cash Acquired			307
Other		0	(2)	1
Net Cash Used in Investing Activities		(855)	(252)	(442)
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs		0	(1)	0
Payments on and repurchases of long-term debt, including current portions and refinancing costs		(11)	(24)	(33)
Increase (decrease) due from affiliates, net		(1,587)	(860)	(297)
Net Cash Provided by (Used in) Financing Activities		(1,598)	(885)	(330)
Effect of Exchange Rates on Cash and Cash Equivalents		(18)	(44)	(22)
Net Change in Cash and Cash Equivalents		(152)	(9)	(65)
Cash and Cash Equivalents at Beginning of Year		261	270
Cash and Cash Equivalents at End of Year		109	261	270
Eliminations
Condensed Consolidating Financial Information
Net Cash Provided by (Used in) Operating Activities		0	0	0
Cash Flows from Investing Activities:
Capital expenditures		0	0	0
Cash related to deconsolidated Venezuela operations		0
Increase (Decrease) in Restricted Cash and Investments		0	0	0
Proceeds from sale of property, plant and equipment and other assets		0	0
Payments to Acquire Businesses, Net of Cash Acquired			0
Other		0	0	0
Net Cash Used in Investing Activities		0	0	0
Cash Flows from Financing Activities:
Long-term debt borrowings, net of issuance costs		0	0	0
Payments on and repurchases of long-term debt, including current portions and refinancing costs		0	0	0
Increase (decrease) due from affiliates, net		0	0	0
Net Cash Provided by (Used in) Financing Activities		0	0	0
Effect of Exchange Rates on Cash and Cash Equivalents		0	0	0
Net Change in Cash and Cash Equivalents		0	0	0
Cash and Cash Equivalents at Beginning of Year		0	0
Cash and Cash Equivalents at End of Year		$ 0	$ 0	$ 0

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