Condensed Consolidating Financial Information - Statements of Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Condensed Consolidating Financial Information
Net cash provided by operating activities	$ 1,123	$ 1,018
INVESTING ACTIVITIES
Capital expenditures	(576)	(546)
Proceeds from sale of property, plant and equipment and other assets	1	119
Net cash used in investing activities	(575)	(427)
FINANCING ACTIVITIES
Distributions	(565)	(605)
Other	(2)	(5)
Increase (decrease) due from/to affiliates, net	0	0
Net cash used in financing activities	(567)	(610)
Net decrease in cash, cash equivalents and restricted cash	(19)	(19)
Cash, cash equivalents and restricted cash at beginning of period	272	331
Cash, cash equivalents and restricted cash at end of period	253	312
Eliminations
Condensed Consolidating Financial Information
Net cash provided by operating activities	0	0
INVESTING ACTIVITIES
Capital expenditures	0	0
Proceeds from sale of property, plant and equipment and other assets	0	0
Net cash used in investing activities	0	0
FINANCING ACTIVITIES
Distributions	0	0
Other	0	0
Increase (decrease) due from/to affiliates, net	0	0
Net cash used in financing activities	0	0
Net decrease in cash, cash equivalents and restricted cash	0	0
Cash, cash equivalents and restricted cash at beginning of period	0	0
Cash, cash equivalents and restricted cash at end of period	0	0
Level 3 Communications, Inc. \| Reportable Legal Entities
Condensed Consolidating Financial Information
Net cash provided by operating activities	(2)	(85)
INVESTING ACTIVITIES
Capital expenditures	0	0
Proceeds from sale of property, plant and equipment and other assets	0	68
Net cash used in investing activities	0	68
FINANCING ACTIVITIES
Distributions	(565)	(605)
Other	0	0
Increase (decrease) due from/to affiliates, net	565	605
Net cash used in financing activities	0	0
Net decrease in cash, cash equivalents and restricted cash	(2)	(17)
Cash, cash equivalents and restricted cash at beginning of period	17	32
Cash, cash equivalents and restricted cash at end of period	15	15
Level 3 Financing, Inc. \| Reportable Legal Entities
Condensed Consolidating Financial Information
Net cash provided by operating activities	0	0
INVESTING ACTIVITIES
Capital expenditures	0	0
Proceeds from sale of property, plant and equipment and other assets	0	0
Net cash used in investing activities	0	0
FINANCING ACTIVITIES
Distributions	0	0
Other	0	0
Increase (decrease) due from/to affiliates, net	0	0
Net cash used in financing activities	0	0
Net decrease in cash, cash equivalents and restricted cash	0	0
Cash, cash equivalents and restricted cash at beginning of period	0	0
Cash, cash equivalents and restricted cash at end of period	0	0
Level 3 Communications, LLC \| Reportable Legal Entities
Condensed Consolidating Financial Information
Net cash provided by operating activities	891	899
INVESTING ACTIVITIES
Capital expenditures	(335)	(289)
Proceeds from sale of property, plant and equipment and other assets	1	0
Net cash used in investing activities	(334)	(289)
FINANCING ACTIVITIES
Distributions	0	0
Other	0	0
Increase (decrease) due from/to affiliates, net	(565)	(605)
Net cash used in financing activities	(565)	(605)
Net decrease in cash, cash equivalents and restricted cash	(8)	5
Cash, cash equivalents and restricted cash at beginning of period	173	186
Cash, cash equivalents and restricted cash at end of period	165	191
Other Non-Guarantor Subsidiaries \| Reportable Legal Entities
Condensed Consolidating Financial Information
Net cash provided by operating activities	234	204
INVESTING ACTIVITIES
Capital expenditures	(241)	(257)
Proceeds from sale of property, plant and equipment and other assets	0	51
Net cash used in investing activities	(241)	(206)
FINANCING ACTIVITIES
Distributions	0	0
Other	(2)	(5)
Increase (decrease) due from/to affiliates, net	0	0
Net cash used in financing activities	(2)	(5)
Net decrease in cash, cash equivalents and restricted cash	(9)	(7)
Cash, cash equivalents and restricted cash at beginning of period	82	113
Cash, cash equivalents and restricted cash at end of period	$ 73	$ 106

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