Supplemental Financial Information Supplemental Financial Information (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains (losses) on marketable securities	$ 6	$ 3
Deferred gains (losses) on cash flow hedges	139	55
Unrecognized gains (losses) on employee benefit obligations	265	325
Cumulative translation adjustments	637	(751)
Accumulated other comprehensive income (loss), net of deferred taxes	1,047	(368)
NBCUniversal Media LLC [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Deferred gains (losses) on cash flow hedges	7	12
Unrecognized gains (losses) on employee benefit obligations	87	140
Cumulative translation adjustments	120	102
Accumulated other comprehensive income (loss), net of deferred taxes	$ 214	$ 254

Amount, after tax, of accumulated unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains or losses.

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount, after tax, of accumulated gain (loss) on derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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