Recent Accounting Pronouncements (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		$ 10,814	$ 9,794
Net cash provided by (used in) financing activities		(3,935)	(1,596)
NBCUniversal Media LLC [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		3,526	2,478
Net cash provided by (used in) financing activities		(2,666)	(1,881)
Financial Assets and Financial Liabilities New Accounting Pronouncement [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New accounting pronouncement impact on net income if adopted	$ (88)	16
Financial Assets and Financial Liabilities New Accounting Pronouncement [Member] | NBCUniversal Media LLC [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New accounting pronouncement impact on net income if adopted	(140)	(139)
Share Based Compensation New Accounting Pronouncement [Member] | Effect of Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in income tax expense	$ 59	$ 198
Increase in diluted earnings per share (in dollars per share)	$ 0.01	$ 0.03
Net cash provided by operating activities		$ 543	411
Net cash provided by (used in) financing activities		$ (543)	$ (411)