Condensed Consolidating Financial Information - Balance Sheets (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Current Assets:
Cash and cash equivalents	$ 507	$ 979	$ 793	$ 918
Restricted cash and securities	7	8
Receivables, less allowances for doubtful accounts	738	714
Due from affiliates	0	0
Other	187	141
Total Current Assets	1,439	1,842
Property, Plant and Equipment, net	8,230	8,199
Restricted Cash and Securities	23	35
Goodwill and Other Intangibles Assets, net	2,790	2,833
Investment in Subsidiaries	0	0
Other Assets, net	370	398
Total Assets	12,852	13,307
Liabilities and Stockholders' Equity:
Accounts payable	633	779
Current portion of long-term debt	21	216
Accrued payroll and employee benefits	212	211
Accrued interest	170	209
Current portion of deferred revenue	219	251
Due to affiliates	0	0
Other	175	136
Total Current Liabilities	1,430	1,802
Long-Term Debt, less current portion	8,537	8,516
Deferred Revenue, less current portion	896	887
Other Liabilities	842	931
Commitments and Contingencies	0	0
Stockholders' Equity (Deficit)	1,147	1,171
Total Liabilities and Stockholders’ Equity (Deficit)	12,852	13,307
Level 3 Communications, Inc.
Current Assets:
Cash and cash equivalents	9	253	296	2
Restricted cash and securities	0	0
Receivables, less allowances for doubtful accounts	0	0
Due from affiliates	15,285	14,446
Other	3	3
Total Current Assets	15,297	14,702
Property, Plant and Equipment, net	0	0
Restricted Cash and Securities	3	12
Goodwill and Other Intangibles Assets, net	0	0
Investment in Subsidiaries	(12,526)	(11,756)
Other Assets, net	13	16
Total Assets	2,787	2,974
Liabilities and Stockholders' Equity:
Accounts payable	0	1
Current portion of long-term debt	0	172
Accrued payroll and employee benefits	0	0
Accrued interest	53	45
Current portion of deferred revenue	0	0
Due to affiliates	0	0
Other	1	1
Total Current Liabilities	54	219
Long-Term Debt, less current portion	1,571	1,570
Deferred Revenue, less current portion	0	0
Other Liabilities	15	14
Commitments and Contingencies	0
Stockholders' Equity (Deficit)	1,147	1,171
Total Liabilities and Stockholders’ Equity (Deficit)	2,787	2,974
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	16,647	15,709
Other	15	16
Total Current Assets	16,668	15,730
Property, Plant and Equipment, net	0	0
Restricted Cash and Securities	0	0
Goodwill and Other Intangibles Assets, net	0	0
Investment in Subsidiaries	(22,242)	(20,470)
Other Assets, net	107	119
Total Assets	(5,467)	(4,621)
Liabilities and Stockholders' Equity:
Accounts payable	1	2
Current portion of long-term debt	0	6
Accrued payroll and employee benefits	0	0
Accrued interest	116	163
Current portion of deferred revenue	0	0
Due to affiliates	0	0
Other	24	1
Total Current Liabilities	141	172
Long-Term Debt, less current portion	6,896	6,886
Deferred Revenue, less current portion	0	0
Other Liabilities	26	81
Commitments and Contingencies	0
Stockholders' Equity (Deficit)	(12,530)	(11,760)
Total Liabilities and Stockholders’ Equity (Deficit)	(5,467)	(4,621)
Level 3 Communications, LLC
Current Assets:
Cash and cash equivalents	289	386	215	618
Restricted cash and securities	1	1
Receivables, less allowances for doubtful accounts	107	93
Due from affiliates	0	0
Other	64	49
Total Current Assets	461	529
Property, Plant and Equipment, net	3,004	2,926
Restricted Cash and Securities	17	17
Goodwill and Other Intangibles Assets, net	404	429
Investment in Subsidiaries	3,921	3,242
Other Assets, net	11	11
Total Assets	7,818	7,154
Liabilities and Stockholders' Equity:
Accounts payable	51	53
Current portion of long-term debt	2	6
Accrued payroll and employee benefits	156	161
Accrued interest	0	0
Current portion of deferred revenue	104	109
Due to affiliates	31,511	30,162
Other	76	29
Total Current Liabilities	31,900	30,520
Long-Term Debt, less current portion	18	20
Deferred Revenue, less current portion	584	602
Other Liabilities	132	75
Commitments and Contingencies	0
Stockholders' Equity (Deficit)	(24,816)	(24,063)
Total Liabilities and Stockholders’ Equity (Deficit)	7,818	7,154
Other Non-Guarantor Subsidiaries
Current Assets:
Cash and cash equivalents	203	335	277	292
Restricted cash and securities	6	7
Receivables, less allowances for doubtful accounts	631	621
Due from affiliates	0	7
Other	105	73
Total Current Assets	945	1,043
Property, Plant and Equipment, net	5,226	5,273
Restricted Cash and Securities	3	6
Goodwill and Other Intangibles Assets, net	2,386	2,404
Investment in Subsidiaries	0	0
Other Assets, net	239	252
Total Assets	8,799	8,978
Liabilities and Stockholders' Equity:
Accounts payable	581	723
Current portion of long-term debt	19	32
Accrued payroll and employee benefits	56	50
Accrued interest	1	1
Current portion of deferred revenue	115	142
Due to affiliates	421	0
Other	74	105
Total Current Liabilities	1,267	1,053
Long-Term Debt, less current portion	52	40
Deferred Revenue, less current portion	312	285
Other Liabilities	669	761
Commitments and Contingencies	0
Stockholders' Equity (Deficit)	6,499	6,839
Total Liabilities and Stockholders’ Equity (Deficit)	8,799	8,978
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	(31,932)	(30,162)
Other	0	0
Total Current Assets	(31,932)	(30,162)
Property, Plant and Equipment, net	0	0
Restricted Cash and Securities	0	0
Goodwill and Other Intangibles Assets, net	0	0
Investment in Subsidiaries	30,847	28,984
Other Assets, net	0	0
Total Assets	(1,085)	(1,178)
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	(31,932)	(30,162)
Other	0	0
Total Current Liabilities	(31,932)	(30,162)
Long-Term Debt, less current portion	0	0
Deferred Revenue, less current portion	0	0
Other Liabilities	0	0
Commitments and Contingencies	0
Stockholders' Equity (Deficit)	30,847	28,984
Total Liabilities and Stockholders’ Equity (Deficit)	$ (1,085)	$ (1,178)