Investments (Investment Income (Loss), Net) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Gains on sales and exchanges of investments, net	$ 3	$ 3	$ 7	$ 176
Investment impairment losses	(15)	(6)	(46)	(30)
Unrealized gains (losses) on securities underlying prepaid forward sale agreements	0	15	42	(13)
Mark to market adjustments on derivative component of prepaid forward sale agreements and indexed debt instruments	(5)	(13)	(42)	19
Interest and dividend income	27	29	83	85
Other, net	(36)	(7)	(20)	17
Investment income (loss), net	(26)	21	24	254
NBCUniversal Media, LLC [Member]
Investment income (loss), net	$ 0	$ 3	$ (4)	$ 18