Stockholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Stockholders' Equity Note [Abstract]
Dividends per common share (in dollars per share)	$ 0.24	$ 0.18	$ 0.72	$ 0.54
Dividends recorded on common stock	$ 150	$ 69	$ 450	$ 205
Class of Stock [Line Items]
Dividends paid per common share (in dollars per share)		$ 0.18		$ 0.54
Class B Common Stock purchased (shares)			1.3
Class B Common Stock purchased			$ 50
Average price per share repurchased (in dollars per share)			$ 38.63
Remaining authorization under repurchase program	$ 2,360		$ 2,360
Dividends per common share (in dollars per share)	$ 0.24	$ 0.18	$ 0.72	$ 0.54
Dividends recorded on common stock	$ 150	$ 69	$ 450	$ 205
Viacom [Member]
Stockholders' Equity Note [Abstract]
Dividends per common share (in dollars per share)		$ 0.20		$ 0.60
Dividends recorded on common stock		$ 82		$ 245
Class of Stock [Line Items]
Dividends paid per common share (in dollars per share)		$ 0.20		$ 0.60
Dividends per common share (in dollars per share)		$ 0.20		$ 0.60
Dividends recorded on common stock		$ 82		$ 245