Condensed Consolidating Financial Information - Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Consolidating Financial Information
Revenue	$ 2,053	$ 2,062	$ 2,061	$ 2,053	$ 1,914	$ 1,629	$ 1,625	$ 1,609	$ 8,229	$ 6,777	$ 6,313
Network Access Costs	708	706	696	723	695	607	613	614	2,833	2,529	2,471
Network Related Expenses	344	369	363	356	345	307	302	292	1,432	1,246	1,214
Costs and Expenses:
Depreciation and Amortization	294	296	288	288	250	187	187	184	1,166	808	800
Selling, General and Administrative Expenses	369	364	364	370	393	266	267	255	1,467	1,181	1,162
Total Costs and Expenses	1,715	1,735	1,711	1,737	1,683	1,367	1,369	1,345	6,898	5,764	5,647
Operating Income (Loss)	338	327	350	316	231	262	256	264	1,331	1,013	666
Other Income (Expense):
Interest Income	0	0	0	1	0	1	0	0	1	1	0
Interest expense	(152)	(145)	(165)	(180)	(195)	(159)	(149)	(151)	(642)	(654)	(649)
Interest income (expense) affiliates, net									0	0	0
Equity in net earnings (losses) of subsidiaries									0	0	0
Other income (expense), net									(407)	(122)	(88)
Total Other Expense	(204)	(310)	(345)	(189)	(268)	(169)	(193)	(145)	(1,048)	(775)	(737)
Income (Loss) Before Income Taxes	134	17	5	127	(37)	93	63	119	283	238	(71)
Income Tax Benefit (Expense)	3,189	(16)	(18)	(5)	103	(8)	(12)	(7)	3,150	76	(38)
Net income (loss)									3,433	314	(109)
Net Income (Loss)	$ 3,323	$ 1	$ (13)	$ 122	$ 66	$ 85	$ 51	$ 112	3,433	314	(109)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									(154)	(183)	10
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									3,279	131	(99)
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									4	21	3
Total Costs and Expenses									4	21	3
Operating Income (Loss)									(4)	(21)	(3)
Other Income (Expense):
Interest Income									0	0	0
Interest expense									(51)	(143)	(151)
Interest income (expense) affiliates, net									1,310	1,227	1,091
Equity in net earnings (losses) of subsidiaries									2,162	(710)	(1,039)
Other income (expense), net									(18)	(53)	0
Total Other Expense									3,403	321	(99)
Income (Loss) Before Income Taxes									3,399	300	(102)
Income Tax Benefit (Expense)									34	14	(7)
Net income (loss)											(109)
Net Income (Loss)									3,433	314
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									(154)	(183)	10
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									3,279	131	(99)
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									0	2	1
Total Costs and Expenses									0	2	1
Operating Income (Loss)									0	(2)	(1)
Other Income (Expense):
Interest Income									0	0	0
Interest expense									(574)	(492)	(497)
Interest income (expense) affiliates, net									1,984	1,827	1,706
Equity in net earnings (losses) of subsidiaries									(1,693)	(2,047)	(2,164)
Other income (expense), net									(200)	0	(85)
Total Other Expense									(483)	(712)	(1,040)
Income (Loss) Before Income Taxes									(483)	(714)	(1,041)
Income Tax Benefit (Expense)									2,645	4	2
Net income (loss)											(1,039)
Net Income (Loss)									2,162	(710)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									0	0	10
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									2,162	(710)	(1,029)
Level 3 Communications, LLC
Condensed Consolidating Financial Information
Revenue									3,325	3,073	2,825
Network Access Costs									1,243	1,177	1,068
Network Related Expenses									947	762	753
Costs and Expenses:
Depreciation and Amortization									309	277	289
Selling, General and Administrative Expenses									1,064	735	791
Total Costs and Expenses									3,563	2,951	2,901
Operating Income (Loss)									(238)	122	(76)
Other Income (Expense):
Interest Income									0	0	0
Interest expense									(3)	(2)	(3)
Interest income (expense) affiliates, net									(3,041)	(2,890)	(2,679)
Equity in net earnings (losses) of subsidiaries									177	663	550
Other income (expense), net									3	7	4
Total Other Expense									(2,864)	(2,222)	(2,128)
Income (Loss) Before Income Taxes									(3,102)	(2,100)	(2,204)
Income Tax Benefit (Expense)									(1)	(1)	0
Net income (loss)											(2,204)
Net Income (Loss)									(3,103)	(2,101)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									0	0	0
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									(3,103)	(2,101)	(2,204)
Other Non-Guarantor Subsidiaries
Condensed Consolidating Financial Information
Revenue									5,077	3,918	3,734
Network Access Costs									1,763	1,566	1,649
Network Related Expenses									485	484	461
Costs and Expenses:
Depreciation and Amortization									857	531	511
Selling, General and Administrative Expenses									399	423	367
Total Costs and Expenses									3,504	3,004	2,988
Operating Income (Loss)									1,573	914	746
Other Income (Expense):
Interest Income									1	1	0
Interest expense									(14)	(17)	2
Interest income (expense) affiliates, net									(253)	(164)	(118)
Equity in net earnings (losses) of subsidiaries									0	0	0
Other income (expense), net									(192)	(76)	(7)
Total Other Expense									(458)	(256)	(123)
Income (Loss) Before Income Taxes									1,115	658	623
Income Tax Benefit (Expense)									472	59	(33)
Net income (loss)											590
Net Income (Loss)									1,587	717
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									154	(183)	10
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									1,741	534	600
Eliminations
Condensed Consolidating Financial Information
Revenue									(173)	(214)	(246)
Network Access Costs									(173)	(214)	(246)
Network Related Expenses									0	0	0
Costs and Expenses:
Depreciation and Amortization									0	0	0
Selling, General and Administrative Expenses									0	0	0
Total Costs and Expenses									(173)	(214)	(246)
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									(646)	2,094	2,653
Other income (expense), net									0	0	0
Total Other Expense									(646)	2,094	2,653
Income (Loss) Before Income Taxes									(646)	2,094	2,653
Income Tax Benefit (Expense)									0	0	0
Net income (loss)											2,653
Net Income (Loss)									(646)	2,094
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									(154)	183	(20)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									$ (800)	$ 2,277	$ 2,633