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Investments (Schedule of Investments) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Equity method	$ 4,007	$ 3,546
Marketable equity securities	451	433
Nonmarketable equity securities	1,279	1,186
Other investments	1,783	1,785
Total investments	7,520	6,950
Less: Current investments	82	19
Noncurrent investments	7,438	6,931
NBCUniversal Media LLC [Member]
Schedule of Investments [Line Items]
Equity method	719	690
Marketable equity securities	385	430
Nonmarketable equity securities	712	696
Total investments	1,816	1,816
Noncurrent investments	$ 1,816	$ 1,816

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