Condensed Consolidating Financial Information - Statements of Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Condensed Consolidating Financial Information
Revenue	$ 2,033			$ 2,062	$ 6,140	$ 6,176
Costs and Expenses:
Network access costs	675			706	2,045	2,125
Network related expenses	337			369	1,014	1,088
Depreciation and amortization	319			296	930	872
Selling, general and administrative Expenses	348			364	1,061	1,098
Total Costs and Expenses	1,679			1,735	5,050	5,183
Operating Income (Loss)	354			327	1,090	993
Other Income (Expense):
Interest income	1			0	3	1
Interest expense	(139)			(145)	(414)	(490)
Interest income (expense) affiliates, net	0			0	0	0
Equity in net earnings (losses) of subsidiaries	0			0	0	0
Other, net	1			(165)	(54)	(355)
Total Other Expense	(137)			(310)	(465)	(844)
Income (Loss) before Income Taxes	217			17	625	149
Income Tax Expense	(74)			(16)	(198)	(39)
Net Income (Loss)	143	$ 156	$ 128	1	427	110
Other Comprehensive Income (Loss), Net of Income Taxes	(15)			(72)	8	(128)
Comprehensive Income (Loss)	128			(71)	435	(18)
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			1	3	3
Total Costs and Expenses	1			1	3	3
Operating Income (Loss)	(1)			(1)	(3)	(3)
Other Income (Expense):
Interest income	0			0	0	0
Interest expense	(9)			(9)	(27)	(42)
Interest income (expense) affiliates, net	342			320	1,027	984
Equity in net earnings (losses) of subsidiaries	(193)			(309)	(581)	(811)
Other, net	0			0	0	(18)
Total Other Expense	140			2	419	113
Income (Loss) before Income Taxes	139			1	416	110
Income Tax Expense	4			0	11	0
Net Income (Loss)	143			1	427	110
Other Comprehensive Income (Loss), Net of Income Taxes	(15)			(72)	8	(128)
Comprehensive Income (Loss)	128			(71)	435	(18)
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	1			0	4	0
Total Costs and Expenses	1			0	4	0
Operating Income (Loss)	(1)			0	(4)	0
Other Income (Expense):
Interest income	0			0	0	0
Interest expense	(124)			(135)	(380)	(436)
Interest income (expense) affiliates, net	526			498	1,585	1,495
Equity in net earnings (losses) of subsidiaries	(539)			(671)	(1,568)	(1,723)
Other, net	0			0	(39)	(145)
Total Other Expense	(137)			(308)	(402)	(809)
Income (Loss) before Income Taxes	(138)			(308)	(406)	(809)
Income Tax Expense	(55)			(1)	(175)	(2)
Net Income (Loss)	(193)			(309)	(581)	(811)
Other Comprehensive Income (Loss), Net of Income Taxes	0			0	0	0
Comprehensive Income (Loss)	(193)			(309)	(581)	(811)
Level 3 Communications, LLC
Condensed Consolidating Financial Information
Revenue	907			830	2,652	2,480
Costs and Expenses:
Network access costs	330			300	965	919
Network related expenses	242			252	716	713
Depreciation and amortization	100			78	280	227
Selling, general and administrative Expenses	262			274	775	789
Total Costs and Expenses	934			904	2,736	2,648
Operating Income (Loss)	(27)			(74)	(84)	(168)
Other Income (Expense):
Interest income	1			0	2	0
Interest expense	(1)			0	(2)	(2)
Interest income (expense) affiliates, net	(804)			(762)	(2,407)	(2,297)
Equity in net earnings (losses) of subsidiaries	169			(186)	569	174
Other, net	(1)			3	2	2
Total Other Expense	(636)			(945)	(1,836)	(2,123)
Income (Loss) before Income Taxes	(663)			(1,019)	(1,920)	(2,291)
Income Tax Expense	0			0	(2)	0
Net Income (Loss)	(663)			(1,019)	(1,922)	(2,291)
Other Comprehensive Income (Loss), Net of Income Taxes	0			0	0	0
Comprehensive Income (Loss)	(663)			(1,019)	(1,922)	(2,291)
Other Non-Guarantor Subsidiaries
Condensed Consolidating Financial Information
Revenue	1,160			1,271	3,590	3,832
Costs and Expenses:
Network access costs	379			445	1,182	1,342
Network related expenses	95			117	298	375
Depreciation and amortization	219			218	650	645
Selling, general and administrative Expenses	84			89	279	306
Total Costs and Expenses	777			869	2,409	2,668
Operating Income (Loss)	383			402	1,181	1,164
Other Income (Expense):
Interest income	0			0	1	1
Interest expense	(5)			(1)	(5)	(10)
Interest income (expense) affiliates, net	(64)			(56)	(205)	(182)
Equity in net earnings (losses) of subsidiaries	0			0	0	0
Other, net	2			(168)	(17)	(194)
Total Other Expense	(67)			(225)	(226)	(385)
Income (Loss) before Income Taxes	316			177	955	779
Income Tax Expense	(23)			(15)	(32)	(37)
Net Income (Loss)	293			162	923	742
Other Comprehensive Income (Loss), Net of Income Taxes	(15)			(72)	8	(128)
Comprehensive Income (Loss)	278			90	931	614
Eliminations
Condensed Consolidating Financial Information
Revenue	(34)			(39)	(102)	(136)
Costs and Expenses:
Network access costs	(34)			(39)	(102)	(136)
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	(34)			(39)	(102)	(136)
Operating Income (Loss)	0			0	0	0
Other Income (Expense):
Interest income	0			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	563			1,166	1,580	2,360
Other, net	0			0	0	0
Total Other Expense	563			1,166	1,580	2,360
Income (Loss) before Income Taxes	563			1,166	1,580	2,360
Income Tax Expense	0			0	0	0
Net Income (Loss)	563			1,166	1,580	2,360
Other Comprehensive Income (Loss), Net of Income Taxes	15			72	(8)	128
Comprehensive Income (Loss)	$ 578			$ 1,238	$ 1,572	$ 2,488