Condensed Consolidating Financial Information - Statements of Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Consolidating Financial Information
Revenue	$ 1,914	$ 1,629	$ 1,625	$ 1,609	$ 1,602	$ 1,569	$ 1,565	$ 1,577	$ 6,777	$ 6,313	$ 6,376
Network Access Costs	695	607	613	614	618	608	616	629	2,529	2,471	2,602
Network Related Expenses	345	307	302	292	298	314	300	302	1,246	1,214	1,249
Costs and Expenses:
Depreciation and Amortization	250	187	187	184	204	203	199	194	808	800	749
Selling, General and Administrative Expenses	393	266	267	255	263	292	310	297	1,181	1,162	1,201
Total Costs and Expenses	1,683	1,367	1,369	1,345	1,383	1,417	1,425	1,422	5,764	5,647	5,801
Operating Income (Loss)	231	262	256	264	219	152	140	155	1,013	666	575
Other Income (Expense):
Interest Income	0	1	0	0	0	0	0	0	1	0	2
Interest expense	(195)	(159)	(149)	(151)	(148)	(165)	(167)	(169)	(654)	(649)	(733)
Interest income (expense) affiliates, net									0	0	0
Equity in net earnings (losses) of subsidiaries									0	0	0
Other income (expense), net									(122)	(88)	(218)
Total Other Expense	(268)	(169)	(193)	(145)	(206)	(159)	(153)	(219)	(775)	(737)	(949)
Income (Loss) Before Income Taxes	(37)	93	63	119	13	(7)	(13)	(64)	238	(71)	(374)
Income Tax Benefit (Expense)	103	(8)	(12)	(7)	1	(14)	(11)	(14)	76	(38)	(48)
Net income (loss)									314	(109)	(422)
Net Income (Loss)	66	85	51	112	14	(21)	(24)	(78)	314	(109)	(422)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									(183)	10	106
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									131	(99)	(316)
Level 3 Communications, Inc.
Condensed Consolidating Financial Information
Revenue									0	0	0
Network Access Costs									0	0	0
Network Related Expenses									0	0	0
Costs and Expenses:
Depreciation and Amortization									0	0	0
Selling, General and Administrative Expenses									21	3	2
Total Costs and Expenses									21	3	2
Operating Income (Loss)									(21)	(3)	(2)
Other Income (Expense):
Interest Income									0	0	0
Interest expense									(143)	(151)	(168)
Interest income (expense) affiliates, net									1,227	1,091	976
Equity in net earnings (losses) of subsidiaries									(710)	(1,039)	(1,188)
Other income (expense), net									(53)	0	(39)
Total Other Expense									321	(99)	(419)
Income (Loss) Before Income Taxes									300	(102)	(421)
Income Tax Benefit (Expense)									14	(7)	(1)
Net income (loss)											(422)
Net Income (Loss)									314	(109)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									(183)	10	106
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									131	(99)	(316)
Level 3 Financing, Inc.
Condensed Consolidating Financial Information
Revenue									0	0	0
Network Access Costs									0	0	0
Network Related Expenses									0	0	0
Costs and Expenses:
Depreciation and Amortization									0	0	0
Selling, General and Administrative Expenses									2	1	1
Total Costs and Expenses									2	1	1
Operating Income (Loss)									(2)	(1)	(1)
Other Income (Expense):
Interest Income									0	0	0
Interest expense									(492)	(497)	(535)
Interest income (expense) affiliates, net									1,827	1,706	1,598
Equity in net earnings (losses) of subsidiaries									(2,047)	(2,164)	(2,066)
Other income (expense), net									0	(85)	(184)
Total Other Expense									(712)	(1,040)	(1,187)
Income (Loss) Before Income Taxes									(714)	(1,041)	(1,188)
Income Tax Benefit (Expense)									4	2	0
Net income (loss)											(1,188)
Net Income (Loss)									(710)	(1,039)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									0	10	106
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									(710)	(1,029)	(1,082)
Level 3 Communications, LLC
Condensed Consolidating Financial Information
Revenue									3,073	2,825	2,657
Network Access Costs									1,177	1,068	996
Network Related Expenses									762	753	741
Costs and Expenses:
Depreciation and Amortization									277	289	260
Selling, General and Administrative Expenses									735	791	818
Total Costs and Expenses									2,951	2,901	2,815
Operating Income (Loss)									122	(76)	(158)
Other Income (Expense):
Interest Income									0	0	1
Interest expense									(2)	(3)	(3)
Interest income (expense) affiliates, net									(2,890)	(2,679)	(2,233)
Equity in net earnings (losses) of subsidiaries									663	550	92
Other income (expense), net									7	4	6
Total Other Expense									(2,222)	(2,128)	(2,137)
Income (Loss) Before Income Taxes									(2,100)	(2,204)	(2,295)
Income Tax Benefit (Expense)									(1)	0	(4)
Net income (loss)											(2,299)
Net Income (Loss)									(2,101)	(2,204)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									0	0	0
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									(2,101)	(2,204)	(2,299)
Other Non-Guarantor Subsidiaries
Condensed Consolidating Financial Information
Revenue									3,918	3,734	3,975
Network Access Costs									1,566	1,649	1,854
Network Related Expenses									484	461	508
Costs and Expenses:
Depreciation and Amortization									531	511	489
Selling, General and Administrative Expenses									423	367	388
Total Costs and Expenses									3,004	2,988	3,239
Operating Income (Loss)									914	746	736
Other Income (Expense):
Interest Income									1	0	1
Interest expense									(17)	2	(27)
Interest income (expense) affiliates, net									(164)	(118)	(341)
Equity in net earnings (losses) of subsidiaries									0	0	0
Other income (expense), net									(76)	(7)	(1)
Total Other Expense									(256)	(123)	(368)
Income (Loss) Before Income Taxes									658	623	368
Income Tax Benefit (Expense)									59	(33)	(43)
Net income (loss)											325
Net Income (Loss)									717	590
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									(183)	10	16
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									534	600	341
Eliminations
Condensed Consolidating Financial Information
Revenue									(214)	(246)	(256)
Network Access Costs									(214)	(246)	(248)
Network Related Expenses									0	0	0
Costs and Expenses:
Depreciation and Amortization									0	0	0
Selling, General and Administrative Expenses									0	0	(8)
Total Costs and Expenses									(214)	(246)	(256)
Operating Income (Loss)									0	0	0
Other Income (Expense):
Interest Income									0	0	0
Interest expense									0	0	0
Interest income (expense) affiliates, net									0	0	0
Equity in net earnings (losses) of subsidiaries									2,094	2,653	3,162
Other income (expense), net									0	0	0
Total Other Expense									2,094	2,653	3,162
Income (Loss) Before Income Taxes									2,094	2,653	3,162
Income Tax Benefit (Expense)									0	0	0
Net income (loss)											3,162
Net Income (Loss)									2,094	2,653
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									183	(20)	(122)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									$ 2,277	$ 2,633	$ 3,040