Recent Accounting Pronouncements (Narrative) (Details) - USD ($) $ in Millions	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 33
NBCUniversal Media LLC [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		0
Member's Capital [Member] \| NBCUniversal Media LLC [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		(232)
AOCI Attributable to Parent [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		76
AOCI Attributable to Parent [Member] \| NBCUniversal Media LLC [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 232
Accounting Standards Update 2016-01 [Member] \| AOCI Attributable to Parent [Member] \| NBCUniversal Media LLC [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 232