Condensed Consolidating Financial Information - Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Condensed Consolidating Financial Information
Net cash provided by operating activities	$ 571
INVESTING ACTIVITIES
Capital expenditures	(252)
Proceeds from sale of property, plant and equipment and other assets	1
Deposits received on assets held for sale	34
Net cash used in investing activities	(217)
Cash Flows from Financing Activities:
Net proceeds from issuance of long-term debt	0
Payments of long-term debt	(1)
Distributions	(390)
Increase (decrease) due from/to affiliates, net	0
Net cash used in financing activities	(391)
Effect of exchange rates on cash, cash equivalents and restricted cash and securities	(1)
Net (decrease) increase in cash, cash equivalents and restricted cash and securities	(38)
Cash, cash equivalents and restricted cash and securities and beginning of period	331
Cash, cash equivalents and restricted cash and securities and end of period	293
Eliminations
Condensed Consolidating Financial Information
Net cash provided by operating activities	0
INVESTING ACTIVITIES
Capital expenditures	0
Proceeds from sale of property, plant and equipment and other assets	0
Deposits received on assets held for sale	0
Net cash used in investing activities	0
Cash Flows from Financing Activities:
Payments of long-term debt	0
Distributions	0
Increase (decrease) due from/to affiliates, net	0
Net cash used in financing activities	0
Effect of exchange rates on cash, cash equivalents and restricted cash and securities	0
Net (decrease) increase in cash, cash equivalents and restricted cash and securities	0
Cash, cash equivalents and restricted cash and securities and beginning of period	0
Cash, cash equivalents and restricted cash and securities and end of period	0
Level 3 Communications, Inc. \| Reportable Legal Entities
Condensed Consolidating Financial Information
Net cash provided by operating activities	(8)
INVESTING ACTIVITIES
Capital expenditures	0
Proceeds from sale of property, plant and equipment and other assets	0
Deposits received on assets held for sale	34
Net cash used in investing activities	34
Cash Flows from Financing Activities:
Payments of long-term debt	0
Distributions	(390)
Increase (decrease) due from/to affiliates, net	390
Net cash used in financing activities	0
Effect of exchange rates on cash, cash equivalents and restricted cash and securities	0
Net (decrease) increase in cash, cash equivalents and restricted cash and securities	26
Cash, cash equivalents and restricted cash and securities and beginning of period	32
Cash, cash equivalents and restricted cash and securities and end of period	58
Level 3 Financing, Inc. \| Reportable Legal Entities
Condensed Consolidating Financial Information
Net cash provided by operating activities	0
INVESTING ACTIVITIES
Capital expenditures	0
Proceeds from sale of property, plant and equipment and other assets	0
Deposits received on assets held for sale	0
Net cash used in investing activities	0
Cash Flows from Financing Activities:
Payments of long-term debt	0
Distributions	0
Increase (decrease) due from/to affiliates, net	0
Net cash used in financing activities	0
Effect of exchange rates on cash, cash equivalents and restricted cash and securities	0
Net (decrease) increase in cash, cash equivalents and restricted cash and securities	0
Cash, cash equivalents and restricted cash and securities and beginning of period	0
Cash, cash equivalents and restricted cash and securities and end of period	0
Level 3 Communications, LLC \| Reportable Legal Entities
Condensed Consolidating Financial Information
Net cash provided by operating activities	490
INVESTING ACTIVITIES
Capital expenditures	(142)
Proceeds from sale of property, plant and equipment and other assets	0
Deposits received on assets held for sale	0
Net cash used in investing activities	(142)
Cash Flows from Financing Activities:
Payments of long-term debt	0
Distributions	0
Increase (decrease) due from/to affiliates, net	(390)
Net cash used in financing activities	(390)
Effect of exchange rates on cash, cash equivalents and restricted cash and securities	0
Net (decrease) increase in cash, cash equivalents and restricted cash and securities	(42)
Cash, cash equivalents and restricted cash and securities and beginning of period	186
Cash, cash equivalents and restricted cash and securities and end of period	144
Other Non-Guarantor Subsidiaries \| Reportable Legal Entities
Condensed Consolidating Financial Information
Net cash provided by operating activities	89
INVESTING ACTIVITIES
Capital expenditures	(110)
Proceeds from sale of property, plant and equipment and other assets	1
Deposits received on assets held for sale	0
Net cash used in investing activities	(109)
Cash Flows from Financing Activities:
Payments of long-term debt	(1)
Distributions	0
Increase (decrease) due from/to affiliates, net	0
Net cash used in financing activities	(1)
Effect of exchange rates on cash, cash equivalents and restricted cash and securities	(1)
Net (decrease) increase in cash, cash equivalents and restricted cash and securities	(22)
Cash, cash equivalents and restricted cash and securities and beginning of period	113
Cash, cash equivalents and restricted cash and securities and end of period	$ 91
Predecessor
Condensed Consolidating Financial Information
Net cash provided by operating activities		$ 539
INVESTING ACTIVITIES
Capital expenditures		(368)
Proceeds from sale of property, plant and equipment and other assets		0
Deposits received on assets held for sale		0
Net cash used in investing activities		(368)
Cash Flows from Financing Activities:
Net proceeds from issuance of long-term debt		4,569
Payments of long-term debt		(4,613)
Distributions		0
Increase (decrease) due from/to affiliates, net		0
Net cash used in financing activities		(44)
Effect of exchange rates on cash, cash equivalents and restricted cash and securities		1
Net (decrease) increase in cash, cash equivalents and restricted cash and securities		128
Cash, cash equivalents and restricted cash and securities and beginning of period		1,857
Cash, cash equivalents and restricted cash and securities and end of period		1,985
Predecessor \| Eliminations
Condensed Consolidating Financial Information
Net cash provided by operating activities		0
INVESTING ACTIVITIES
Capital expenditures		0
Net cash used in investing activities		0
Cash Flows from Financing Activities:
Net proceeds from issuance of long-term debt		0
Payments of long-term debt		0
Increase (decrease) due from/to affiliates, net		0
Net cash used in financing activities		0
Effect of exchange rates on cash, cash equivalents and restricted cash and securities		0
Net (decrease) increase in cash, cash equivalents and restricted cash and securities		0
Cash, cash equivalents and restricted cash and securities and beginning of period		0
Cash, cash equivalents and restricted cash and securities and end of period		0
Predecessor \| Level 3 Communications, Inc. \| Reportable Legal Entities
Condensed Consolidating Financial Information
Net cash provided by operating activities		(16)
INVESTING ACTIVITIES
Capital expenditures		0
Net cash used in investing activities		0
Cash Flows from Financing Activities:
Net proceeds from issuance of long-term debt		0
Payments of long-term debt		0
Increase (decrease) due from/to affiliates, net		16
Net cash used in financing activities		16
Effect of exchange rates on cash, cash equivalents and restricted cash and securities		0
Net (decrease) increase in cash, cash equivalents and restricted cash and securities		0
Cash, cash equivalents and restricted cash and securities and beginning of period		37
Cash, cash equivalents and restricted cash and securities and end of period		37
Predecessor \| Level 3 Financing, Inc. \| Reportable Legal Entities
Condensed Consolidating Financial Information
Net cash provided by operating activities		(135)
INVESTING ACTIVITIES
Capital expenditures		0
Net cash used in investing activities		0
Cash Flows from Financing Activities:
Net proceeds from issuance of long-term debt		4,569
Payments of long-term debt		(4,611)
Increase (decrease) due from/to affiliates, net		177
Net cash used in financing activities		135
Effect of exchange rates on cash, cash equivalents and restricted cash and securities		0
Net (decrease) increase in cash, cash equivalents and restricted cash and securities		0
Cash, cash equivalents and restricted cash and securities and beginning of period		0
Cash, cash equivalents and restricted cash and securities and end of period		0
Predecessor \| Level 3 Communications, LLC \| Reportable Legal Entities
Condensed Consolidating Financial Information
Net cash provided by operating activities		109
INVESTING ACTIVITIES
Capital expenditures		(233)
Net cash used in investing activities		(233)
Cash Flows from Financing Activities:
Net proceeds from issuance of long-term debt		0
Payments of long-term debt		0
Increase (decrease) due from/to affiliates, net		262
Net cash used in financing activities		262
Effect of exchange rates on cash, cash equivalents and restricted cash and securities		0
Net (decrease) increase in cash, cash equivalents and restricted cash and securities		138
Cash, cash equivalents and restricted cash and securities and beginning of period		1,710
Cash, cash equivalents and restricted cash and securities and end of period		1,848
Predecessor \| Other Non-Guarantor Subsidiaries \| Reportable Legal Entities
Condensed Consolidating Financial Information
Net cash provided by operating activities		581
INVESTING ACTIVITIES
Capital expenditures		(135)
Net cash used in investing activities		(135)
Cash Flows from Financing Activities:
Net proceeds from issuance of long-term debt		0
Payments of long-term debt		(2)
Increase (decrease) due from/to affiliates, net		(455)
Net cash used in financing activities		(457)
Effect of exchange rates on cash, cash equivalents and restricted cash and securities		1
Net (decrease) increase in cash, cash equivalents and restricted cash and securities		(10)
Cash, cash equivalents and restricted cash and securities and beginning of period		110
Cash, cash equivalents and restricted cash and securities and end of period		$ 100

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