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Investments (Marketable Equity Securities) (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended	6 Months Ended
	Mar. 31, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Schedule of Marketable Equity Securities [Line Items]
Marketable equity securities			$ 451	$ 451		$ 433
NBCUniversal Media LLC [Member]
Schedule of Marketable Equity Securities [Line Items]
Contribution from member					$ 662
Marketable equity securities			385	385		430
Snap [Member]
Schedule of Marketable Equity Securities [Line Items]
Payments to acquire marketable securities		$ 500
Marketable equity securities			385	385		430
Marketable securities, recognized unrealized gains (losses)			(82)	(45)
Snap [Member] | NBCUniversal Media LLC [Member]
Schedule of Marketable Equity Securities [Line Items]
Contribution from member	$ 662
Marketable equity securities			385	385		$ 430
Marketable securities, recognized unrealized gains (losses)			$ (82)	$ (45)

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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-Publisher FASB
-Name Accounting Standards Codification
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Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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