Condensed Consolidating Financial Information - Balance Sheets (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Current Assets:
Cash and cash equivalents	$ 1,056	$ 1,819	$ 1,291	$ 854
Marketable Securities	1,127	0
Restricted cash and securities	5	7
Receivables, less allowances for doubtful accounts	707	712
Due from affiliates	0	0
Other	141	115
Total Current Assets	3,036	2,653
Property, Plant and Equipment, net	10,392	10,139
Restricted Cash and Securities	29	31
Goodwill and Other Intangibles Assets, net	8,546	8,644
Investment in Subsidiaries	0	0
Deferred Tax Assets	3,235	3,370
Other Assets, net	49	51
Total Assets	25,287	24,888
Liabilities and Stockholders' Equity:
Accounts payable	693	706
Current portion of long-term debt	306	7
Accrued payroll and employee benefits	178	195
Accrued interest	97	129
Current portion of deferred revenue	262	266
Due to affiliates	0	0
Other	162	168
Total Current Liabilities	1,698	1,471
Long-Term Debt, less current portion	10,584	10,877
Deferred Revenue, less current portion	1,058	1,001
Other Liabilities	632	622
Commitments and Contingencies
Stockholders' Equity (Deficit)	11,315	10,917
Total Liabilities and Stockholders’ Equity	25,287	24,888
Level 3 Communications, Inc.
Current Assets:
Cash and cash equivalents	14	15	11	12
Marketable Securities	0
Restricted cash and securities	0	0
Receivables, less allowances for doubtful accounts	0	0
Due from affiliates	17,832	17,032
Other	0	0
Total Current Assets	17,846	17,047
Property, Plant and Equipment, net	0	0
Restricted Cash and Securities	19	22
Goodwill and Other Intangibles Assets, net	0	0
Investment in Subsidiaries	16,926	16,869
Deferred Tax Assets	55	51
Other Assets, net	0	0
Total Assets	34,846	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	11	11
Current portion of deferred revenue	0	0
Due to affiliates	0	0
Other	0	0
Total Current Liabilities	11	11
Long-Term Debt, less current portion	593	592
Deferred Revenue, less current portion	0	0
Other Liabilities	16	16
Commitments and Contingencies
Stockholders' Equity (Deficit)	34,226	33,370
Total Liabilities and Stockholders’ Equity	34,846	33,989
Level 3 Financing, Inc.
Current Assets:
Cash and cash equivalents	0	0	6	6
Marketable Securities	0
Restricted cash and securities	0	0
Receivables, less allowances for doubtful accounts	0	0
Due from affiliates	22,581	21,715
Other	0	0
Total Current Assets	22,581	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	17,664	17,599
Deferred Tax Assets	2,617	2,687
Other Assets, net	0	0
Total Assets	42,862	42,001
Liabilities and Stockholders' Equity:
Accounts payable	1	0
Current portion of long-term debt	299	0
Accrued payroll and employee benefits	0	0
Accrued interest	79	110
Current portion of deferred revenue	0	0
Due to affiliates	0	0
Other	(1)	0
Total Current Liabilities	378	110
Long-Term Debt, less current portion	9,816	10,108
Deferred Revenue, less current portion	0	0
Other Liabilities	0	0
Commitments and Contingencies
Stockholders' Equity (Deficit)	32,668	31,783
Total Liabilities and Stockholders’ Equity	42,862	42,001
Level 3 Communications, LLC
Current Assets:
Cash and cash equivalents	938	1,700	1,202	727
Marketable Securities	1,127
Restricted cash and securities	1	1
Receivables, less allowances for doubtful accounts	4	26
Due from affiliates	0	0
Other	116	87
Total Current Assets	2,186	1,814
Property, Plant and Equipment, net	4,105	3,869
Restricted Cash and Securities	10	9
Goodwill and Other Intangibles Assets, net	352	353
Investment in Subsidiaries	3,639	3,674
Deferred Tax Assets	(1)	0
Other Assets, net	14	16
Total Assets	10,305	9,735
Liabilities and Stockholders' Equity:
Accounts payable	324	307
Current portion of long-term debt	2	2
Accrued payroll and employee benefits	149	160
Accrued interest	0	0
Current portion of deferred revenue	111	116
Due to affiliates	43,237	40,927
Other	130	127
Total Current Liabilities	43,953	41,639
Long-Term Debt, less current portion	12	13
Deferred Revenue, less current portion	781	719
Other Liabilities	164	155
Commitments and Contingencies
Stockholders' Equity (Deficit)	(34,605)	(32,791)
Total Liabilities and Stockholders’ Equity	10,305	9,735
Other Non-Guarantor Subsidiaries
Current Assets:
Cash and cash equivalents	104	104	72	109
Marketable Securities	0
Restricted cash and securities	4	6
Receivables, less allowances for doubtful accounts	703	686
Due from affiliates	2,824	2,180
Other	25	28
Total Current Assets	3,660	3,004
Property, Plant and Equipment, net	6,287	6,270
Restricted Cash and Securities	0	0
Goodwill and Other Intangibles Assets, net	8,194	8,291
Investment in Subsidiaries	0	0
Deferred Tax Assets	564	632
Other Assets, net	35	35
Total Assets	18,740	18,232
Liabilities and Stockholders' Equity:
Accounts payable	368	399
Current portion of long-term debt	5	5
Accrued payroll and employee benefits	29	35
Accrued interest	7	8
Current portion of deferred revenue	151	150
Due to affiliates	0	0
Other	33	41
Total Current Liabilities	593	638
Long-Term Debt, less current portion	163	164
Deferred Revenue, less current portion	277	282
Other Liabilities	452	451
Commitments and Contingencies
Stockholders' Equity (Deficit)	17,255	16,697
Total Liabilities and Stockholders’ Equity	18,740	18,232
Eliminations
Current Assets:
Cash and cash equivalents	0	0	$ 0	$ 0
Marketable Securities	0
Restricted cash and securities	0	0
Receivables, less allowances for doubtful accounts	0	0
Due from affiliates	(43,237)	(40,927)
Other	0	0
Total Current Assets	(43,237)	(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	(38,229)	(38,142)
Deferred Tax Assets	0	0
Other Assets, net	0	0
Total Assets	(81,466)	(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	(43,237)	(40,927)
Other	0	0
Total Current Liabilities	(43,237)	(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)	(38,229)	(38,142)
Total Liabilities and Stockholders’ Equity	$ (81,466)	$ (79,069)