Condensed Consolidating Financial Information - Balance Sheets (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Current Assets:
Cash and cash equivalents	$ 1,947	$ 1,819	$ 1,004	$ 854
Restricted cash and securities	7	7
Receivables, less allowances for doubtful accounts	712	712
Due from affiliates	0	0
Other	141	115
Total Current Assets	2,807	2,653
Property, Plant and Equipment, net	10,285	10,139
Restricted Cash and Securities	31	31
Goodwill and Other Intangibles Assets, net	8,592	8,644
Investment in Subsidiaries	0	0
Deferred Tax Assets	3,305	3,370
Other Assets, net	51	51
Total Assets	25,071	24,888
Liabilities and Stockholders' Equity:
Accounts payable	750	706
Current portion of long-term debt	307	7
Accrued payroll and employee benefits	148	195
Accrued interest	101	129
Current portion of deferred revenue	275	266
Due to affiliates	0	0
Other	153	168
Total Current Liabilities	1,734	1,471
Long-Term Debt, less current portion	10,581	10,877
Deferred Revenue, less current portion	1,044	1,001
Other Liabilities	631	622
Commitments and Contingencies
Stockholders' Equity (Deficit)	11,081	10,917
Total Liabilities and Stockholders’ Equity	25,071	24,888
Level 3 Communications, Inc.
Current Assets:
Cash and cash equivalents	15	15	12	12
Restricted cash and securities	0	0
Receivables, less allowances for doubtful accounts	0	0
Due from affiliates	17,415	17,032
Other	0	0
Total Current Assets	17,430	17,047
Property, Plant and Equipment, net	0	0
Restricted Cash and Securities	22	22
Goodwill and Other Intangibles Assets, net	0	0
Investment in Subsidiaries	16,899	16,869
Deferred Tax Assets	53	51
Other Assets, net	0	0
Total Assets	34,404	33,989
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	592
Deferred Revenue, less current portion	0	0
Other Liabilities	16	16
Commitments and Contingencies
Stockholders' Equity (Deficit)	33,793	33,370
Total Liabilities and Stockholders’ Equity	34,404	33,989
Level 3 Financing, Inc.
Current Assets:
Cash and cash equivalents	0	0	6	6
Restricted cash and securities	0	0
Receivables, less allowances for doubtful accounts	0	0
Due from affiliates	22,142	21,715
Other	0	0
Total Current Assets	22,142	21,715
Property, Plant and Equipment, net	0	0
Restricted Cash and Securities	0	0
Goodwill and Other Intangibles Assets, net	0	0
Investment in Subsidiaries	17,610	17,599
Deferred Tax Assets	2,650	2,687
Other Assets, net	0	0
Total Assets	42,402	42,001
Liabilities and Stockholders' Equity:
Accounts payable	3	0
Current portion of long-term debt	299	0
Accrued payroll and employee benefits	0	0
Accrued interest	91	110
Current portion of deferred revenue	0	0
Due to affiliates	0	0
Other	1	0
Total Current Liabilities	394	110
Long-Term Debt, less current portion	9,813	10,108
Deferred Revenue, less current portion	0	0
Other Liabilities	0	0
Commitments and Contingencies
Stockholders' Equity (Deficit)	32,195	31,783
Total Liabilities and Stockholders’ Equity	42,402	42,001
Level 3 Communications, LLC
Current Assets:
Cash and cash equivalents	1,838	1,700	886	727
Restricted cash and securities	1	1
Receivables, less allowances for doubtful accounts	18	26
Due from affiliates	0	0
Other	111	87
Total Current Assets	1,968	1,814
Property, Plant and Equipment, net	4,012	3,869
Restricted Cash and Securities	9	9
Goodwill and Other Intangibles Assets, net	352	353
Investment in Subsidiaries	3,655	3,674
Deferred Tax Assets	(1)	0
Other Assets, net	15	16
Total Assets	10,010	9,735
Liabilities and Stockholders' Equity:
Accounts payable	346	307
Current portion of long-term debt	2	2
Accrued payroll and employee benefits	112	160
Accrued interest	0	0
Current portion of deferred revenue	114	116
Due to affiliates	42,088	40,927
Other	125	127
Total Current Liabilities	42,787	41,639
Long-Term Debt, less current portion	12	13
Deferred Revenue, less current portion	760	719
Other Liabilities	160	155
Commitments and Contingencies
Stockholders' Equity (Deficit)	(33,709)	(32,791)
Total Liabilities and Stockholders’ Equity	10,010	9,735
Other Non-Guarantor Subsidiaries
Current Assets:
Cash and cash equivalents	94	104	100	109
Restricted cash and securities	6	6
Receivables, less allowances for doubtful accounts	694	686
Due from affiliates	2,531	2,180
Other	30	28
Total Current Assets	3,355	3,004
Property, Plant and Equipment, net	6,273	6,270
Restricted Cash and Securities	0	0
Goodwill and Other Intangibles Assets, net	8,240	8,291
Investment in Subsidiaries	0	0
Deferred Tax Assets	603	632
Other Assets, net	36	35
Total Assets	18,507	18,232
Liabilities and Stockholders' Equity:
Accounts payable	401	399
Current portion of long-term debt	6	5
Accrued payroll and employee benefits	36	35
Accrued interest	7	8
Current portion of deferred revenue	161	150
Due to affiliates	0	0
Other	27	41
Total Current Liabilities	638	638
Long-Term Debt, less current portion	164	164
Deferred Revenue, less current portion	284	282
Other Liabilities	455	451
Commitments and Contingencies
Stockholders' Equity (Deficit)	16,966	16,697
Total Liabilities and Stockholders’ Equity	18,507	18,232
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	(42,088)	(40,927)
Other	0	0
Total Current Assets	(42,088)	(40,927)
Property, Plant and Equipment, net	0	0
Restricted Cash and Securities	0	0
Goodwill and Other Intangibles Assets, net	0	0
Investment in Subsidiaries	(38,164)	(38,142)
Deferred Tax Assets	0	0
Other Assets, net	0	0
Total Assets	(80,252)	(79,069)
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	(42,088)	(40,927)
Other	0	0
Total Current Liabilities	(42,088)	(40,927)
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)	(38,164)	(38,142)
Total Liabilities and Stockholders’ Equity	$ (80,252)	$ (79,069)