Unaudited Quarterly Financial Data (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended			3 Months Ended	0 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	Mar. 31, 2012	Oct. 04, 2013	Dec. 31, 2011	Aug. 12, 2014
Selected Quarterly Financial Information [Abstract]
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
Operating Income (Loss)	231	262	256	264	219	152	140	155	1,013	666	575
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)
Net Income (Loss)	66	85	51	112	14	(21)	(24)	(78)	314	(109)	(422)
Earnings Per Share, Basic	$ 0.22	$ 0.36	$ 0.21	$ 0.48	$ 0.06	$ (0.09)	$ (0.11)	$ (0.36)	$ 1.23	$ (0.49)	$ (1.96)
Earnings Per Share, Diluted	$ 0.21	$ 0.35	$ 0.21	$ 0.47	$ 0.06	$ (0.09)	$ (0.11)	$ (0.36)	$ 1.21	$ (0.49)	$ (1.96)
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
Depreciation expense									713	727	659
Depreciation and Amortization	250	187	187	184	204	203	199	194	808	800	749
Impairment of Intangible Assets (Excluding Goodwill)									17
Loss on modification and extinguishment of debt, net	(53)	0	0	0	(67)	(17)	0	0	(53)	(84)	(160)
Business Combination, Integration Related Costs	70								81
Other, net	(20)	(11)	(44)	6	9	23	14	(50)	(69)	(4)	(58)
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 Expense (Benefit)	(103)	8	12	7	(1)	14	11	14	(76)	38	48
Recognized Income Tax Benefit	100
Foreign Currency Transaction Gain (Loss), before Tax			34					22
Foreign Currency Exchange Rate, Translation			6.3					6.30			4.30
Foreign Currency Exchange Rate, Remeasurement			10.6
Property, Plant and Equipment, Gross	19,489				17,329				19,489	17,329
Long-term Debt, Gross	11,366				8,392				11,366	8,392
Asset Retirement Obligation, Revision of Estimate									7	0
Tranche B-II Term Loans and Senior Notes [Member]
Selected Quarterly Financial Information [Abstract]
Loss on modification and extinguishment of debt, net	53
Senior Notes 11 Point 875 Percent Due 2019 [Member]
Selected Quarterly Financial Information [Abstract]
Debt instrument, stated interest rate (as a percent)	11.875%								11.875%					11.875%
Long-term Debt, Gross	0				605				0	605
TrancheB2022TermLoanTotal [Member]
Selected Quarterly Financial Information [Abstract]
Long-term Debt, Gross	2,000								2,000
Senior Notes 5.375percent Due 2022 [Member]
Selected Quarterly Financial Information [Abstract]
Debt Instrument, Face Amount	1,000.0								1,000.0						1,000.0
Debt instrument, stated interest rate (as a percent)	5.375%								5.375%
TrancheBII2019TermLoan [Member]
Selected Quarterly Financial Information [Abstract]
Loss on modification and extinguishment of debt, net					10
Senior Notes 10 Point 0 Percent Due 2018 [Member]
Selected Quarterly Financial Information [Abstract]
Loss on modification and extinguishment of debt, net					56
Debt instrument, stated interest rate (as a percent)	10.00%				10.00%				10.00%	10.00%				10.00%
Floating Rate Senior Notes due 2015 [Member]
Selected Quarterly Financial Information [Abstract]
Loss on modification and extinguishment of debt, net					1
Debt instrument, stated interest rate (as a percent)	3.846%								3.846%					4.202%
Tranche A Term Loan
Selected Quarterly Financial Information [Abstract]
Loss on modification and extinguishment of debt, net		(9)
Tranche B II and Tranche B III Term Loans
Selected Quarterly Financial Information [Abstract]
Loss on modification and extinguishment of debt, net	(50)				(67)
Senior Notes due 2017 (8.75%)
Selected Quarterly Financial Information [Abstract]
Loss on modification and extinguishment of debt, net		(40)
Debt instrument, stated interest rate (as a percent)														8.75%
Convertible Senior Notes due 2013 (15.0%)
Selected Quarterly Financial Information [Abstract]
Debt instrument, stated interest rate (as a percent)	15.00%								15.00%					15.00%
Senior Notes due 2014 (9.25%)
Selected Quarterly Financial Information [Abstract]
Loss on modification and extinguishment of debt, net												(22)
Debt instrument, stated interest rate (as a percent)														9.25%
Asset Retirement Obligation Change in Estimate
Selected Quarterly Financial Information [Abstract]
Selling, General and Administrative Expenses											47
Total Costs and Expenses										49
Depreciation and Amortization											2
Property, Plant and Equipment, Gross											24
Level 3 Escrow II, Inc. [Member] | Senior Notes 5.375percent Due 2022 [Member]
Selected Quarterly Financial Information [Abstract]
Debt Instrument, Face Amount															1,000.0
Guarantor Subsidiaries [Member]
Selected Quarterly Financial Information [Abstract]
Revenue									0	0	0
Network Access Costs									0	0	0
Network Related Expenses									0	0	0
Operating Income (Loss)									(2)	(1)	(1)
Interest Income									0	0	0
Interest Expense									(492)	(497)	(535)
Net Income (Loss)									(710)	(1,039)
Selling, General and Administrative Expenses									2	1	1
Total Costs and Expenses									2	1	1
Depreciation and Amortization									0	0	0
Total Other Expense									(712)	(1,040)	(1,187)
Income (Loss) Before Income Taxes									(714)	(1,041)	(1,188)
Income Tax Expense (Benefit)									(4)	(2)	0
Guarantor Subsidiaries [Member] | TrancheB2022TermLoanTotal [Member]
Selected Quarterly Financial Information [Abstract]
Long-term Debt, Gross	2,000								2,000
Guarantor Subsidiaries [Member] | TrancheBII2019TermLoan [Member]
Selected Quarterly Financial Information [Abstract]
Loss on modification and extinguishment of debt, net													$ 10