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Investments (Marketable Equity Securities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Schedule of Marketable Equity Securities [Line Items]
Marketable equity securities	$ 538		$ 341
NBCUniversal Media LLC [Member]
Schedule of Marketable Equity Securities [Line Items]
Marketable equity securities	324		162
Snap [Member]
Schedule of Marketable Equity Securities [Line Items]
Marketable securities, recognized unrealized gains (losses)	162	$ 37
Marketable equity securities	324		162
Snap [Member] | NBCUniversal Media LLC [Member]
Schedule of Marketable Equity Securities [Line Items]
Marketable securities, recognized unrealized gains (losses)	162	$ 37
Marketable equity securities	$ 324		$ 162

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[Line Items] for Schedule of Fair Value Method Investments [Table]

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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

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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).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117546-209714

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