Condensed Consolidating Financial Information - Statements of Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Condensed Consolidating Financial Information
Revenue	$ 2,048	$ 2,051
Costs and Expenses:
Network access costs	691	694
Network related expenses	336	338
Depreciation and amortization	320	301
Selling, general and administrative Expenses	364	356
Total Costs and Expenses	1,711	1,689
Operating Income (Loss)	337	362
Other Income (Expense):
Interest income	2	1
Interest expense	(134)	(135)
Interest income (expense) affiliates, net	0	0
Equity in net earnings (losses) of subsidiaries	0	0
Other, net	(40)	(10)
Total Other Expense	(172)	(144)
Income (Loss) before Income Taxes	165	218
Income Tax Expense	(70)	(90)
Net Income (Loss)	95	128
Other Comprehensive Income (Loss), Net of Income Taxes	21	45
Comprehensive Income (Loss)	116	173
Level 3 Communications, Inc.
Condensed Consolidating Financial Information
Revenue	0	0
Costs and Expenses:
Network access costs	0	0
Network related expenses	0	0
Depreciation and amortization	0	0
Selling, general and administrative Expenses	1	1
Total Costs and Expenses	1	1
Operating Income (Loss)	(1)	(1)
Other Income (Expense):
Interest income	0	0
Interest expense	(9)	(9)
Interest income (expense) affiliates, net	377	342
Equity in net earnings (losses) of subsidiaries	(275)	(212)
Other, net	0	0
Total Other Expense	93	121
Income (Loss) before Income Taxes	92	120
Income Tax Expense	3	4
Net Income (Loss)	95	124
Other Comprehensive Income (Loss), Net of Income Taxes	21	45
Comprehensive Income (Loss)	116	169
Level 3 Financing, Inc.
Condensed Consolidating Financial Information
Revenue	0	0
Costs and Expenses:
Network access costs	0	0
Network related expenses	0	0
Depreciation and amortization	0	0
Selling, general and administrative Expenses	1	1
Total Costs and Expenses	1	1
Operating Income (Loss)	(1)	(1)
Other Income (Expense):
Interest income	0	0
Interest expense	(120)	(128)
Interest income (expense) affiliates, net	574	531
Equity in net earnings (losses) of subsidiaries	(646)	(541)
Other, net	(44)	0
Total Other Expense	(236)	(138)
Income (Loss) before Income Taxes	(237)	(139)
Income Tax Expense	(38)	(69)
Net Income (Loss)	(275)	(208)
Other Comprehensive Income (Loss), Net of Income Taxes	0	0
Comprehensive Income (Loss)	(275)	(208)
Level 3 Communications, LLC
Condensed Consolidating Financial Information
Revenue	920	866
Costs and Expenses:
Network access costs	323	320
Network related expenses	243	237
Depreciation and amortization	104	88
Selling, general and administrative Expenses	277	250
Total Costs and Expenses	947	895
Operating Income (Loss)	(27)	(29)
Other Income (Expense):
Interest income	2	0
Interest expense	(1)	(1)
Interest income (expense) affiliates, net	(869)	(801)
Equity in net earnings (losses) of subsidiaries	203	199
Other, net	5	2
Total Other Expense	(660)	(601)
Income (Loss) before Income Taxes	(687)	(630)
Income Tax Expense	(1)	(1)
Net Income (Loss)	(688)	(631)
Other Comprehensive Income (Loss), Net of Income Taxes	0	0
Comprehensive Income (Loss)	(688)	(631)
Other Non-Guarantor Subsidiaries
Condensed Consolidating Financial Information
Revenue	1,157	1,219
Costs and Expenses:
Network access costs	397	408
Network related expenses	93	101
Depreciation and amortization	216	213
Selling, general and administrative Expenses	85	104
Total Costs and Expenses	791	826
Operating Income (Loss)	366	393
Other Income (Expense):
Interest income	0	1
Interest expense	(4)	3
Interest income (expense) affiliates, net	(82)	(72)
Equity in net earnings (losses) of subsidiaries	0	0
Other, net	(1)	(12)
Total Other Expense	(87)	(80)
Income (Loss) before Income Taxes	279	313
Income Tax Expense	(34)	(24)
Net Income (Loss)	245	289
Other Comprehensive Income (Loss), Net of Income Taxes	21	45
Comprehensive Income (Loss)	266	334
Eliminations
Condensed Consolidating Financial Information
Revenue	(29)	(34)
Costs and Expenses:
Network access costs	(29)	(34)
Network related expenses	0	0
Depreciation and amortization	0	0
Selling, general and administrative Expenses	0	0
Total Costs and Expenses	(29)	(34)
Operating Income (Loss)	0	0
Other Income (Expense):
Interest income	0	0
Interest expense	0	0
Interest income (expense) affiliates, net	0	0
Equity in net earnings (losses) of subsidiaries	718	554
Other, net	0	0
Total Other Expense	718	554
Income (Loss) before Income Taxes	718	554
Income Tax Expense	0	0
Net Income (Loss)	718	554
Other Comprehensive Income (Loss), Net of Income Taxes	(21)	(45)
Comprehensive Income (Loss)	$ 697	$ 509