Condensed Consolidating Financial Information - Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Current Assets:
Cash and cash equivalents	$ 691	$ 580	$ 729	$ 631
Restricted cash and securities	7	7
Receivables, less allowances for doubtful accounts	810	737
Due from affiliates	0	0
Other	155	165
Total Current Assets	1,663	1,489
Property, Plant and Equipment, net	9,812	9,860
Restricted Cash and Securities	44	20
Goodwill and Other Intangibles Assets, net	8,935	9,103
Investment in Subsidiaries	0	0
Other Assets, net	429	475
Total Assets	20,883	20,947
Liabilities and Stockholders' Equity:
Accounts payable	630	664
Current portion of long-term debt	16	349
Accrued payroll and employee benefits	230	273
Accrued interest	137	174
Current portion of deferred revenue	273	287
Due to affiliates	0	0
Other	184	167
Total Current Liabilities	1,470	1,914
Long-Term Debt, less current portion	10,997	10,984
Deferred Revenue, less current portion	942	921
Other Liabilities	$ 694	$ 765
Commitments and Contingencies
Stockholders' Equity (Deficit)	$ 6,780	$ 6,363
Total Liabilities and Stockholders’ Equity (Deficit)	20,883	20,947
Level 3 Communications, Inc.
Current Assets:
Cash and cash equivalents	13	7	7	8
Restricted cash and securities	0	0
Receivables, less allowances for doubtful accounts	0	0
Due from affiliates	15,304	14,522
Other	1	2
Total Current Assets	15,318	14,531
Property, Plant and Equipment, net	0	0
Restricted Cash and Securities	27	3
Goodwill and Other Intangibles Assets, net	0	0
Investment in Subsidiaries	16,737	16,686
Other Assets, net	20	28
Total Assets	32,102	31,248
Liabilities and Stockholders' Equity:
Accounts payable	0	0
Current portion of long-term debt	0	333
Accrued payroll and employee benefits	0	0
Accrued interest	3	12
Current portion of deferred revenue	0	0
Due to affiliates	0	0
Other	0	0
Total Current Liabilities	3	345
Long-Term Debt, less current portion	600	900
Deferred Revenue, less current portion	0	0
Other Liabilities	$ 15	$ 16
Commitments and Contingencies
Stockholders' Equity (Deficit)	$ 31,484	$ 29,987
Total Liabilities and Stockholders’ Equity (Deficit)	32,102	31,248
Level 3 Financing, Inc.
Current Assets:
Cash and cash equivalents	6	5	5	6
Restricted cash and securities	0	0
Receivables, less allowances for doubtful accounts	0	0
Due from affiliates	22,482	21,270
Other	19	21
Total Current Assets	22,507	21,296
Property, Plant and Equipment, net	0	0
Restricted Cash and Securities	0	0
Goodwill and Other Intangibles Assets, net	0	0
Investment in Subsidiaries	14,542	14,777
Other Assets, net	119	129
Total Assets	37,168	36,202
Liabilities and Stockholders' Equity:
Accounts payable	1	0
Current portion of long-term debt	0	0
Accrued payroll and employee benefits	0	0
Accrued interest	128	158
Current portion of deferred revenue	0	0
Due to affiliates	0	0
Other	0	2
Total Current Liabilities	129	160
Long-Term Debt, less current portion	10,209	9,893
Deferred Revenue, less current portion	0	0
Other Liabilities	$ 27	$ 24
Commitments and Contingencies
Stockholders' Equity (Deficit)	$ 26,803	$ 26,125
Total Liabilities and Stockholders’ Equity (Deficit)	37,168	36,202
Level 3 Communications, LLC
Current Assets:
Cash and cash equivalents	559	307	524	347
Restricted cash and securities	1	1
Receivables, less allowances for doubtful accounts	68	34
Due from affiliates	0	0
Other	67	45
Total Current Assets	695	387
Property, Plant and Equipment, net	3,320	3,152
Restricted Cash and Securities	15	16
Goodwill and Other Intangibles Assets, net	365	373
Investment in Subsidiaries	3,737	3,729
Other Assets, net	11	9
Total Assets	8,143	7,666
Liabilities and Stockholders' Equity:
Accounts payable	194	215
Current portion of long-term debt	3	3
Accrued payroll and employee benefits	198	174
Accrued interest	0	0
Current portion of deferred revenue	113	118
Due to affiliates	36,981	34,401
Other	94	62
Total Current Liabilities	37,583	34,973
Long-Term Debt, less current portion	15	16
Deferred Revenue, less current portion	648	617
Other Liabilities	$ 132	$ 125
Commitments and Contingencies
Stockholders' Equity (Deficit)	$ (30,235)	$ (28,065)
Total Liabilities and Stockholders’ Equity (Deficit)	8,143	7,666
Other Non-Guarantor Subsidiaries
Current Assets:
Cash and cash equivalents	113	261	193	270
Restricted cash and securities	6	6
Receivables, less allowances for doubtful accounts	742	703
Due from affiliates	0	0
Other	68	97
Total Current Assets	929	1,067
Property, Plant and Equipment, net	6,492	6,708
Restricted Cash and Securities	2	1
Goodwill and Other Intangibles Assets, net	8,570	8,730
Investment in Subsidiaries	0	0
Other Assets, net	279	309
Total Assets	16,272	16,815
Liabilities and Stockholders' Equity:
Accounts payable	435	449
Current portion of long-term debt	13	13
Accrued payroll and employee benefits	32	99
Accrued interest	6	4
Current portion of deferred revenue	160	169
Due to affiliates	805	1,391
Other	90	103
Total Current Liabilities	1,541	2,228
Long-Term Debt, less current portion	173	175
Deferred Revenue, less current portion	294	304
Other Liabilities	$ 520	$ 600
Commitments and Contingencies
Stockholders' Equity (Deficit)	$ 13,744	$ 13,508
Total Liabilities and Stockholders’ Equity (Deficit)	16,272	16,815
Eliminations
Current Assets:
Cash and cash equivalents	0	0	$ 0	$ 0
Restricted cash and securities	0	0
Receivables, less allowances for doubtful accounts	0	0
Due from affiliates	(37,786)	(35,792)
Other	0	0
Total Current Assets	(37,786)	(35,792)
Property, Plant and Equipment, net	0	0
Restricted Cash and Securities	0	0
Goodwill and Other Intangibles Assets, net	0	0
Investment in Subsidiaries	(35,016)	(35,192)
Other Assets, net	0	0
Total Assets	(72,802)	(70,984)
Liabilities and Stockholders' Equity:
Accounts payable	0	0
Current portion of long-term debt	0	0
Accrued payroll and employee benefits	0	0
Accrued interest	0	0
Current portion of deferred revenue	0	0
Due to affiliates	(37,786)	(35,792)
Other	0	0
Total Current Liabilities	(37,786)	(35,792)
Long-Term Debt, less current portion	0	0
Deferred Revenue, less current portion	0	0
Other Liabilities	$ 0	$ 0
Commitments and Contingencies
Stockholders' Equity (Deficit)	$ (35,016)	$ (35,192)
Total Liabilities and Stockholders’ Equity (Deficit)	$ (72,802)	$ (70,984)