Condensed Consolidating Financial Information - Statements of Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Condensed Consolidating Financial Information
Revenue	$ 2,062	$ 1,629	$ 6,176	$ 4,863
Costs and Expenses:
Network Access Costs	706	607	2,125	1,834
Network Related Expenses	369	307	1,088	901
Depreciation and Amortization	296	187	872	558
Selling, General and Administrative Expenses	364	266	1,098	788
Total Costs and Expenses	1,735	1,367	5,183	4,081
Operating Income (Loss)	327	262	993	782
Other Income (Expense):
Interest Income	0	1	1	1
Interest expense	(145)	(159)	(490)	(459)
Interest income (expense) affiliates, net	0	0	0	0
Equity in net earnings (losses) of subsidiaries	0	0	0	0
Other, net	(165)	(11)	(355)	(49)
Total Other Expense	(310)	(169)	(844)	(507)
Income (Loss) before Income Taxes	17	93	149	275
Income Tax Expense	(16)	(8)	(39)	(27)
Net Income (Loss)	1	85	110	248
Other Comprehensive Income (Loss), Net of Income Taxes	(72)	(137)	(128)	(118)
Comprehensive Income (Loss)	(71)	(52)	(18)	130
Level 3 Communications, Inc.
Condensed Consolidating Financial Information
Revenue	0	0	0	0
Costs and Expenses:
Network Access Costs	0	0	0	0
Network Related Expenses	0	0	0	0
Depreciation and Amortization	0	0	0	0
Selling, General and Administrative Expenses	1	6	3	7
Total Costs and Expenses	1	6	3	7
Operating Income (Loss)	(1)	(6)	(3)	(7)
Other Income (Expense):
Interest Income		0	0	0
Interest expense	(9)	(34)	(42)	(102)
Interest income (expense) affiliates, net	320	314	984	905
Equity in net earnings (losses) of subsidiaries	(309)	(189)	(811)	(548)
Other, net	0	0	(18)	0
Total Other Expense	2	91	113	255
Income (Loss) before Income Taxes	1	85	110	248
Income Tax Expense	0	0	0	0
Net Income (Loss)	1	85	110	248
Other Comprehensive Income (Loss), Net of Income Taxes	(72)	(137)	(128)	(118)
Comprehensive Income (Loss)	(71)	(52)	(18)	130
Level 3 Financing, Inc.
Condensed Consolidating Financial Information
Revenue	0	0	0	0
Costs and Expenses:
Network Access Costs	0	0	0	0
Network Related Expenses	0	0	0	0
Depreciation and Amortization	0	0	0	0
Selling, General and Administrative Expenses	0	0	0	1
Total Costs and Expenses	0	0	0	1
Operating Income (Loss)	0	0	0	(1)
Other Income (Expense):
Interest Income		0	0	0
Interest expense	(135)	(112)	(436)	(337)
Interest income (expense) affiliates, net	498	452	1,495	1,370
Equity in net earnings (losses) of subsidiaries	(671)	(528)	(1,723)	(1,577)
Other, net	0	0	(145)	0
Total Other Expense	(308)	(188)	(809)	(544)
Income (Loss) before Income Taxes	(308)	(188)	(809)	(545)
Income Tax Expense	(1)	(1)	(2)	(3)
Net Income (Loss)	(309)	(189)	(811)	(548)
Other Comprehensive Income (Loss), Net of Income Taxes	0	0	0	0
Comprehensive Income (Loss)	(309)	(189)	(811)	(548)
Level 3 Communications, LLC
Condensed Consolidating Financial Information
Revenue	830	781	2,478	2,278
Costs and Expenses:
Network Access Costs	300	291	919	869
Network Related Expenses	252	195	713	567
Depreciation and Amortization	78	70	227	209
Selling, General and Administrative Expenses	274	181	789	505
Total Costs and Expenses	904	737	2,648	2,150
Operating Income (Loss)	(74)	44	(170)	128
Other Income (Expense):
Interest Income		0	0	0
Interest expense	0	(1)	(2)	(1)
Interest income (expense) affiliates, net	(763)	(730)	(2,298)	(2,169)
Equity in net earnings (losses) of subsidiaries	0	162	177	502
Other, net	3	2	2	6
Total Other Expense	(760)	(567)	(2,121)	(1,662)
Income (Loss) before Income Taxes	(834)	(523)	(2,291)	(1,534)
Income Tax Expense	0	0	0	(1)
Net Income (Loss)	(834)	(523)	(2,291)	(1,535)
Other Comprehensive Income (Loss), Net of Income Taxes	0	0	0	0
Comprehensive Income (Loss)	(834)	(523)	(2,291)	(1,535)
Other Non-Guarantor Subsidiaries
Condensed Consolidating Financial Information
Revenue	1,271	901	3,834	2,750
Costs and Expenses:
Network Access Costs	445	369	1,342	1,130
Network Related Expenses	117	112	375	334
Depreciation and Amortization	218	117	645	349
Selling, General and Administrative Expenses	89	79	306	275
Total Costs and Expenses	869	677	2,668	2,088
Operating Income (Loss)	402	224	1,166	662
Other Income (Expense):
Interest Income		1	1	1
Interest expense	(1)	(12)	(10)	(19)
Interest income (expense) affiliates, net	(55)	(36)	(181)	(106)
Equity in net earnings (losses) of subsidiaries	0	0	0	0
Other, net	(168)	(13)	(194)	(55)
Total Other Expense	(224)	(60)	(384)	(179)
Income (Loss) before Income Taxes	178	164	782	483
Income Tax Expense	(15)	(7)	(37)	(23)
Net Income (Loss)	163	157	745	460
Other Comprehensive Income (Loss), Net of Income Taxes	72	(137)	128	(118)
Comprehensive Income (Loss)	235	20	873	342
Eliminations
Condensed Consolidating Financial Information
Revenue	(39)	(53)	(136)	(165)
Costs and Expenses:
Network Access Costs	(39)	(53)	(136)	(165)
Network Related Expenses	0	0	0	0
Depreciation and Amortization	0	0	0	0
Selling, General and Administrative Expenses	0	0	0	0
Total Costs and Expenses	(39)	(53)	(136)	(165)
Operating Income (Loss)	0	0	0	0
Other Income (Expense):
Interest Income		0	0	0
Interest expense	0	0	0	0
Interest income (expense) affiliates, net	0	0	0	0
Equity in net earnings (losses) of subsidiaries	980	555	2,357	1,623
Other, net	0	0	0	0
Total Other Expense	980	555	2,357	1,623
Income (Loss) before Income Taxes	980	555	2,357	1,623
Income Tax Expense	0	0	0	0
Net Income (Loss)	980	555	2,357	1,623
Other Comprehensive Income (Loss), Net of Income Taxes	(72)	137	(128)	118
Comprehensive Income (Loss)	$ 908	$ 692	$ 2,229	$ 1,741