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Supplemental Financial Information (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains (losses) on marketable securities	$ 4		$ 1
Deferred gains (losses) on cash flow hedges	54		20
Unrecognized gains (losses) on employee benefit obligations	318		310
Cumulative translation adjustments	46		277
Accumulated other comprehensive income (loss), net of deferred taxes	422	$ (368)	608
NBCUniversal Media LLC [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Deferred gains (losses) on cash flow hedges	11		(3)
Unrecognized gains (losses) on employee benefit obligations	138		122
Cumulative translation adjustments	73		277
Accumulated other comprehensive income (loss), net of deferred taxes	$ 222	$ 254	$ 396

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Accumulated unrealized gain (loss), after tax, 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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