Condensed Consolidating Financial Information - Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Current Assets:
Cash and cash equivalents	$ 1,569	$ 854	$ 691	$ 580
Restricted cash and securities	8	8
Receivables, less allowances for doubtful accounts	749	757
Due from affiliates	0	0
Other	131	111
Total Current Assets	2,457	1,730
Property, Plant and Equipment, net	10,167	9,878
Restricted Cash and Securities	31	42
Goodwill and Other Intangibles Assets, net	8,703	8,876
Investment in Subsidiaries	0	0
Deferred Tax Assets	3,339	3,441
Other Assets, net	49	50
Total Assets	24,746	24,017
Liabilities and Stockholders' Equity:
Accounts payable	728	629
Current portion of long-term debt	7	15
Accrued payroll and employee benefits	194	218
Accrued interest	135	108
Current portion of deferred revenue	263	267
Due to affiliates	0	0
Other	180	179
Total Current Liabilities	1,507	1,416
Long-Term Debt, less current portion	10,875	10,866
Deferred Revenue, less current portion	1,010	977
Other Liabilities	630	632
Commitments and Contingencies
Stockholders' Equity (Deficit)	10,724	10,126
Total Liabilities and Stockholders’ Equity (Deficit)	24,746	24,017
Level 3 Communications, Inc.
Current Assets:
Cash and cash equivalents	16	12	13	7
Restricted cash and securities	0	0
Receivables, less allowances for doubtful accounts	0	0
Due from affiliates	16,717	12,415
Other	0	0
Total Current Assets	16,733	12,427
Property, Plant and Equipment, net	0	0
Restricted Cash and Securities	22	27
Goodwill and Other Intangibles Assets, net	0	0
Investment in Subsidiaries	16,846	16,772
Deferred Tax Assets	48	38
Other Assets, net	0	0
Total Assets	33,649	29,264
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	3	11
Current portion of deferred revenue	0	0
Due to affiliates	0	0
Other	0	0
Total Current Liabilities	3	11
Long-Term Debt, less current portion	592	591
Deferred Revenue, less current portion	0	0
Other Liabilities	15	15
Commitments and Contingencies
Stockholders' Equity (Deficit)	33,039	28,647
Total Liabilities and Stockholders’ Equity (Deficit)	33,649	29,264
Level 3 Financing, Inc.
Current Assets:
Cash and cash equivalents	0	6	6	5
Restricted cash and securities	0	0
Receivables, less allowances for doubtful accounts	0	0
Due from affiliates	20,980	22,759
Other	0	0
Total Current Assets	20,980	22,765
Property, Plant and Equipment, net	0	0
Restricted Cash and Securities	0	0
Goodwill and Other Intangibles Assets, net	0	0
Investment in Subsidiaries	17,692	17,714
Deferred Tax Assets	2,713	2,847
Other Assets, net	0	0
Total Assets	41,385	43,326
Liabilities and Stockholders' Equity:
Accounts payable	0	1
Current portion of long-term debt	0	0
Accrued payroll and employee benefits	0	0
Accrued interest	124	90
Current portion of deferred revenue	0	0
Due to affiliates	0	0
Other	0	0
Total Current Liabilities	124	91
Long-Term Debt, less current portion	10,103	10,092
Deferred Revenue, less current portion	0	0
Other Liabilities	0	0
Commitments and Contingencies
Stockholders' Equity (Deficit)	31,158	33,143
Total Liabilities and Stockholders’ Equity (Deficit)	41,385	43,326
Level 3 Communications, LLC
Current Assets:
Cash and cash equivalents	1,482	727	559	307
Restricted cash and securities	1	1
Receivables, less allowances for doubtful accounts	41	47
Due from affiliates	0	0
Other	89	56
Total Current Assets	1,613	831
Property, Plant and Equipment, net	3,780	3,423
Restricted Cash and Securities	9	14
Goodwill and Other Intangibles Assets, net	355	363
Investment in Subsidiaries	3,691	3,734
Deferred Tax Assets	0	0
Other Assets, net	12	12
Total Assets	9,460	8,377
Liabilities and Stockholders' Equity:
Accounts payable	367	195
Current portion of long-term debt	2	2
Accrued payroll and employee benefits	160	186
Accrued interest	0	0
Current portion of deferred revenue	113	119
Due to affiliates	40,551	37,990
Other	138	115
Total Current Liabilities	41,331	38,607
Long-Term Debt, less current portion	13	15
Deferred Revenue, less current portion	724	680
Other Liabilities	148	133
Commitments and Contingencies
Stockholders' Equity (Deficit)	(32,756)	(31,058)
Total Liabilities and Stockholders’ Equity (Deficit)	9,460	8,377
Other Non-Guarantor Subsidiaries
Current Assets:
Cash and cash equivalents	71	109	113	261
Restricted cash and securities	7	7
Receivables, less allowances for doubtful accounts	708	710
Due from affiliates	2,854	2,816
Other	42	55
Total Current Assets	3,682	3,697
Property, Plant and Equipment, net	6,387	6,455
Restricted Cash and Securities	0	1
Goodwill and Other Intangibles Assets, net	8,348	8,513
Investment in Subsidiaries	0	0
Deferred Tax Assets	578	556
Other Assets, net	37	38
Total Assets	19,032	19,260
Liabilities and Stockholders' Equity:
Accounts payable	361	433
Current portion of long-term debt	5	13
Accrued payroll and employee benefits	34	32
Accrued interest	8	7
Current portion of deferred revenue	150	148
Due to affiliates	0	0
Other	42	64
Total Current Liabilities	600	697
Long-Term Debt, less current portion	167	168
Deferred Revenue, less current portion	286	297
Other Liabilities	467	484
Commitments and Contingencies
Stockholders' Equity (Deficit)	17,512	17,614
Total Liabilities and Stockholders’ Equity (Deficit)	19,032	19,260
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	(40,551)	(37,990)
Other	0	0
Total Current Assets	(40,551)	(37,990)
Property, Plant and Equipment, net	0	0
Restricted Cash and Securities	0	0
Goodwill and Other Intangibles Assets, net	0	0
Investment in Subsidiaries	(38,229)	(38,220)
Deferred Tax Assets	0	0
Other Assets, net	0	0
Total Assets	(78,780)	(76,210)
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	(40,551)	(37,990)
Other	0	0
Total Current Liabilities	(40,551)	(37,990)
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)	(38,229)	(38,220)
Total Liabilities and Stockholders’ Equity (Deficit)	$ (78,780)	$ (76,210)