Segment Information (Reconciliation of Adjusted EBITDA from Segment to Consolidated Statements) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Adjusted EBITDA	$ 7,417	$ 7,075	$ 14,661	$ 14,085
Depreciation	(2,021)	(1,970)	(4,032)	(3,885)
Amortization	(582)	(537)	(1,170)	(1,090)
Other operating gains	200	0	200	0
Interest expense	(806)	(758)	(1,583)	(1,513)
Investment and other income (loss), net	77	99	203	229
Income before income taxes	4,285	3,909	8,279	7,826
NBCUniversal Media LLC [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Adjusted EBITDA	2,160	2,074	4,445	4,093
Depreciation	(258)	(265)	(500)	(496)
Amortization	(295)	(255)	(563)	(532)
Interest expense	(133)	(149)	(260)	(292)
Investment and other income (loss), net	(168)	(15)	(172)	(16)
Income before income taxes	$ 1,306	$ 1,390	$ 2,950	$ 2,757

The measure used to evaluate the profitability of operating segments.

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The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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Amount of gain (loss) on sale or disposal of assets, including but not limited to property plant and equipment, intangible assets and equity in securities of subsidiaries or equity method investee.

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Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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Amount of the cost of borrowed funds accounted for as interest expense.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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