Acquisition of Level 3 - Preliminary Estimated Aggregate Consideration (Details) - USD ($) $ in Millions		9 Months Ended
Nov. 01, 2017	Sep. 30, 2018	Dec. 31, 2017
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Goodwill		$ 30,770	$ 30,475
Level 3 Parent, LLC
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Cash, accounts receivable and other current assets		3,292	3,317
Property, plant and equipment		9,397	9,311
Other noncurrent assets		985	782
Current liabilities, excluding current maturities of long-term debt		(1,492)	(1,461)
Current maturities of long-term debt		(7)	(7)
Long-term debt		(10,888)	(10,888)
Deferred revenue and other liabilities		(1,731)	(1,629)
Goodwill		11,190	10,837
Total estimated aggregate consideration		19,612	19,617
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustments [Abstract]
Cash, accounts receivable and other current assets		(25)
Property, plant and equipment		86
Other noncurrent assets		203
Current liabilities, excluding current maturities of long-term debt		(31)
Current maturities of long-term debt		0
Long-term debt		0
Deferred revenue and other liabilities		(102)
Goodwill		353
Total estimated aggregate consideration		(5)
Accounts receivable contractual value	$ 884	884
Weighted average useful life	12 years
Level 3 Parent, LLC \| Customer relationships
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Identifiable intangible assets		8,488	8,964
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustments [Abstract]
Identifiable intangible assets		(476)
Level 3 Parent, LLC \| Other intangible assets
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract]
Identifiable intangible assets		378	$ 391
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustments [Abstract]
Identifiable intangible assets		$ (13)

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Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Current Liabilities, Excluding Long-term Debt

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Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Current Liabilities, Long-Term Debt

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Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Accounts Receivable Contractual Value

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Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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This element represents the amount of any measurement period adjustment (as defined) realized during the reporting period to items of consideration transferred in connection with a business combination for which the initial accounting was incomplete.

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Amount of assets that are expected to be realized or consumed within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Amount of long-term debt due within one year or within the normal operating cycle, if longer, assumed at the acquisition date.

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The amount of identifiable intangible assets recognized as of the acquisition date.

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Amount of long-term debt due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

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Amount of other assets expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Amount recognized for assets, including goodwill, in excess of (less than) the aggregate liabilities assumed.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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