Condensed Consolidating Financial Information - Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Consolidating Financial Information
Revenue	$ 2,032	$ 2,033	$ 2,056	$ 2,051	$ 2,053	$ 2,062	$ 2,061	$ 2,053	$ 8,172	$ 8,229	$ 6,777
Network Access Costs	680	675	676	694	708	706	696	723	2,725	2,833	2,529
Network Related Expenses	332	337	339	338	344	369	363	356	1,346	1,432	1,246
Costs and Expenses:
Depreciation and Amortization	320	319	310	301	294	296	288	288	1,250	1,166	808
Selling, General and Administrative Expenses	346	348	357	356	369	364	364	370	1,407	1,467	1,181
Total Costs and Expenses	1,678	1,679	1,682	1,689	1,715	1,735	1,711	1,737	6,728	6,898	5,764
Operating Income (Loss)	354	354	374	362	338	327	350	316	1,444	1,331	1,013
Other Income (Expense):
Interest Income	1	1	1	1	0	0	0	1	4	1	1
Interest expense	(132)	(139)	(140)	(135)	(152)	(145)	(165)	(180)	(546)	(642)	(654)
Interest income (expense) affiliates, net									0	0	0
Equity in net earnings (losses) of subsidiaries									0	0	0
Other income (expense), net									(60)	(407)	(122)
Total Other Expense	(137)	(137)	(184)	(144)	(204)	(310)	(345)	(189)	(602)	(1,048)	(775)
Income (Loss) Before Income Taxes	217	217	190	218	134	17	5	127	842	283	238
Income Tax Benefit (Expense)	33	(74)	(34)	(90)	3,189	(16)	(18)	(5)	(165)	3,150	76
Net income (loss)											314
Net Income	$ 250	$ 143	$ 156	$ 128	$ 3,323	$ 1	$ (13)	$ 122	677	3,433	314
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									(86)	(154)	(183)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									591	3,279	131
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									16	4	21
Total Costs and Expenses									16	4	21
Operating Income (Loss)									(16)	(4)	(21)
Other Income (Expense):
Interest Income									0	0	0
Interest expense									(36)	(51)	(143)
Interest income (expense) affiliates, net									1,385	1,310	1,227
Equity in net earnings (losses) of subsidiaries									(669)	2,162	(710)
Other income (expense), net									(1)	(18)	(53)
Total Other Expense									679	3,403	321
Income (Loss) Before Income Taxes									663	3,399	300
Income Tax Benefit (Expense)									14	34	14
Net income (loss)											314
Net Income									677	3,433
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									(86)	(154)	(183)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									591	3,279	131
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									5	0	2
Total Costs and Expenses									5	0	2
Operating Income (Loss)									(5)	0	(2)
Other Income (Expense):
Interest Income									0	0	0
Interest expense									(505)	(574)	(492)
Interest income (expense) affiliates, net									2,113	1,984	1,827
Equity in net earnings (losses) of subsidiaries									(2,033)	(1,693)	(2,047)
Other income (expense), net									(39)	(200)	0
Total Other Expense									(464)	(483)	(712)
Income (Loss) Before Income Taxes									(469)	(483)	(714)
Income Tax Benefit (Expense)									(200)	2,645	4
Net income (loss)											(710)
Net Income									(669)	2,162
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									0	0	0
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									(669)	2,162	(710)
Level 3 Communications, LLC
Condensed Consolidating Financial Information
Revenue									3,557	3,325	3,073
Network Access Costs									1,283	1,243	1,177
Network Related Expenses									953	947	762
Costs and Expenses:
Depreciation and Amortization									385	309	277
Selling, General and Administrative Expenses									1,024	1,064	735
Total Costs and Expenses									3,645	3,563	2,951
Operating Income (Loss)									(88)	(238)	122
Other Income (Expense):
Interest Income									3	0	0
Interest expense									(2)	(3)	(2)
Interest income (expense) affiliates, net									(3,215)	(3,041)	(2,890)
Equity in net earnings (losses) of subsidiaries									757	177	663
Other income (expense), net									2	3	7
Total Other Expense									(2,455)	(2,864)	(2,222)
Income (Loss) Before Income Taxes									(2,543)	(3,102)	(2,100)
Income Tax Benefit (Expense)									(2)	(1)	(1)
Net income (loss)											(2,101)
Net Income									(2,545)	(3,103)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									0	0	0
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									(2,545)	(3,103)	(2,101)
Other Non-Guarantor Subsidiaries
Condensed Consolidating Financial Information
Revenue									4,747	5,077	3,918
Network Access Costs									1,574	1,763	1,566
Network Related Expenses									393	485	484
Costs and Expenses:
Depreciation and Amortization									865	857	531
Selling, General and Administrative Expenses									362	399	423
Total Costs and Expenses									3,194	3,504	3,004
Operating Income (Loss)									1,553	1,573	914
Other Income (Expense):
Interest Income									1	1	1
Interest expense									(3)	(14)	(17)
Interest income (expense) affiliates, net									(283)	(253)	(164)
Equity in net earnings (losses) of subsidiaries									0	0	0
Other income (expense), net									(22)	(192)	(76)
Total Other Expense									(307)	(458)	(256)
Income (Loss) Before Income Taxes									1,246	1,115	658
Income Tax Benefit (Expense)									23	472	59
Net income (loss)											717
Net Income									1,269	1,587
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									(86)	(154)	(183)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									1,183	1,433	534
Eliminations
Condensed Consolidating Financial Information
Revenue									(132)	(173)	(214)
Network Access Costs									(132)	(173)	(214)
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									(132)	(173)	(214)
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									1,945	(646)	2,094
Other income (expense), net									0	0	0
Total Other Expense									1,945	(646)	2,094
Income (Loss) Before Income Taxes									1,945	(646)	2,094
Income Tax Benefit (Expense)									0	0	0
Net income (loss)											2,094
Net Income									1,945	(646)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent									86	154	183
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									$ 2,031	$ (492)	$ 2,277